[PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator.

[PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Introduce any context BPF specific memory allocator.

Tracing BPF programs can attach to kprobe and fentry. Hence they
run in unknown context where calling plain kmalloc() might not be safe.
Front-end kmalloc() with per-cpu cache of free elements.
Refill this cache asynchronously from irq_work.

Major achievements enabled by bpf_mem_alloc:
- Dynamically allocated hash maps used to be 10 times slower than fully preallocated.
  With bpf_mem_alloc and subsequent optimizations the speed of dynamic maps is equal to full prealloc.
- Tracing bpf programs can use dynamically allocated hash maps.
  Potentially saving lots of memory. Typical hash map is sparsely populated.
- Sleepable bpf programs can used dynamically allocated hash maps.

v2->v3:
- Rewrote the free_list algorithm based on discussions with Kumar. Patch 1.
- Allowed sleepable bpf progs use dynamically allocated maps. Patches 13 and 14.
- Added sysctl to force bpf_mem_alloc in hash map even if pre-alloc is
  requested to reduce memory consumption. Patch 15.
- Fix: zero-fill percpu allocation
- Single rcu_barrier at the end instead of each cpu during bpf_mem_alloc destruction

v2 thread:
https://lore.kernel.org/bpf/20220817210419.95560-1-alexei.starovoitov@gmail.com/

v1->v2:
- Moved unsafe direct call_rcu() from hash map into safe place inside bpf_mem_alloc. Patches 7 and 9.
- Optimized atomic_inc/dec in hash map with percpu_counter. Patch 6.
- Tuned watermarks per allocation size. Patch 8
- Adopted this approach to per-cpu allocation. Patch 10.
- Fully converted hash map to bpf_mem_alloc. Patch 11.
- Removed tracing prog restriction on map types. Combination of all patches and final patch 12.

v1 thread:
https://lore.kernel.org/bpf/20220623003230.37497-1-alexei.starovoitov@gmail.com/

LWN article:
https://lwn.net/Articles/899274/

Future work:
- expose bpf_mem_alloc as uapi FD to be used in dynptr_alloc, kptr_alloc
- convert lru map to bpf_mem_alloc

Alexei Starovoitov (15):
  bpf: Introduce any context BPF specific memory allocator.
  bpf: Convert hash map to bpf_mem_alloc.
  selftests/bpf: Improve test coverage of test_maps
  samples/bpf: Reduce syscall overhead in map_perf_test.
  bpf: Relax the requirement to use preallocated hash maps in tracing
    progs.
  bpf: Optimize element count in non-preallocated hash map.
  bpf: Optimize call_rcu in non-preallocated hash map.
  bpf: Adjust low/high watermarks in bpf_mem_cache
  bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.
  bpf: Add percpu allocation support to bpf_mem_alloc.
  bpf: Convert percpu hash map to per-cpu bpf_mem_alloc.
  bpf: Remove tracing program restriction on map types
  bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.
  bpf: Remove prealloc-only restriction for sleepable bpf programs.
  bpf: Introduce sysctl kernel.bpf_force_dyn_alloc.

 include/linux/bpf_mem_alloc.h             |  26 +
 include/linux/filter.h                    |   2 +
 kernel/bpf/Makefile                       |   2 +-
 kernel/bpf/core.c                         |   2 +
 kernel/bpf/hashtab.c                      | 132 +++--
 kernel/bpf/memalloc.c                     | 601 ++++++++++++++++++++++
 kernel/bpf/syscall.c                      |  14 +-
 kernel/bpf/verifier.c                     |  52 --
 samples/bpf/map_perf_test_kern.c          |  44 +-
 samples/bpf/map_perf_test_user.c          |   2 +-
 tools/testing/selftests/bpf/progs/timer.c |  11 -
 tools/testing/selftests/bpf/test_maps.c   |  38 +-
 12 files changed, 795 insertions(+), 131 deletions(-)
 create mode 100644 include/linux/bpf_mem_alloc.h
 create mode 100644 kernel/bpf/memalloc.c

-- 
2.30.2

[PATCH v3 bpf-next 01/15] bpf: Introduce any context BPF specific memory allocator.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Tracing BPF programs can attach to kprobe and fentry. Hence they
run in unknown context where calling plain kmalloc() might not be safe.

Front-end kmalloc() with minimal per-cpu cache of free elements.
Refill this cache asynchronously from irq_work.

BPF programs always run with migration disabled.
It's safe to allocate from cache of the current cpu with irqs disabled.
Free-ing is always done into bucket of the current cpu as well.
irq_work trims extra free elements from buckets with kfree
and refills them with kmalloc, so global kmalloc logic takes care
of freeing objects allocated by one cpu and freed on another.

struct bpf_mem_alloc supports two modes:
- When size != 0 create kmem_cache and bpf_mem_cache for each cpu.
  This is typical bpf hash map use case when all elements have equal size.
- When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
  kmalloc/kfree. Max allocation size is 4096 in this case.
  This is bpf_dynptr and bpf_kptr use case.

bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree.
bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free.

The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/bpf_mem_alloc.h |  26 ++
 kernel/bpf/Makefile           |   2 +-
 kernel/bpf/memalloc.c         | 475 ++++++++++++++++++++++++++++++++++
 3 files changed, 502 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/bpf_mem_alloc.h
 create mode 100644 kernel/bpf/memalloc.c

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
new file mode 100644
index 000000000000..804733070f8d
--- /dev/null
+++ b/include/linux/bpf_mem_alloc.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+#ifndef _BPF_MEM_ALLOC_H
+#define _BPF_MEM_ALLOC_H
+#include <linux/compiler_types.h>
+
+struct bpf_mem_cache;
+struct bpf_mem_caches;
+
+struct bpf_mem_alloc {
+	struct bpf_mem_caches __percpu *caches;
+	struct bpf_mem_cache __percpu *cache;
+};
+
+int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size);
+void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
+
+/* kmalloc/kfree equivalent: */
+void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size);
+void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
+
+/* kmem_cache_alloc/free equivalent: */
+void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
+void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
+
+#endif /* _BPF_MEM_ALLOC_H */
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 057ba8e01e70..11fb9220909b 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -13,7 +13,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
-obj-$(CONFIG_BPF_SYSCALL) += btf.o
+obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o
 obj-$(CONFIG_BPF_JIT) += dispatcher.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
new file mode 100644
index 000000000000..293380eaea41
--- /dev/null
+++ b/kernel/bpf/memalloc.c
@@ -0,0 +1,475 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+#include <linux/mm.h>
+#include <linux/llist.h>
+#include <linux/bpf.h>
+#include <linux/irq_work.h>
+#include <linux/bpf_mem_alloc.h>
+#include <linux/memcontrol.h>
+
+/* Any context (including NMI) BPF specific memory allocator.
+ *
+ * Tracing BPF programs can attach to kprobe and fentry. Hence they
+ * run in unknown context where calling plain kmalloc() might not be safe.
+ *
+ * Front-end kmalloc() with per-cpu per-bucket cache of free elements.
+ * Refill this cache asynchronously from irq_work.
+ *
+ * CPU_0 buckets
+ * 16 32 64 96 128 196 256 512 1024 2048 4096
+ * ...
+ * CPU_N buckets
+ * 16 32 64 96 128 196 256 512 1024 2048 4096
+ *
+ * The buckets are prefilled at the start.
+ * BPF programs always run with migration disabled.
+ * It's safe to allocate from cache of the current cpu with irqs disabled.
+ * Free-ing is always done into bucket of the current cpu as well.
+ * irq_work trims extra free elements from buckets with kfree
+ * and refills them with kmalloc, so global kmalloc logic takes care
+ * of freeing objects allocated by one cpu and freed on another.
+ *
+ * Every allocated objected is padded with extra 8 bytes that contains
+ * struct llist_node.
+ */
+#define LLIST_NODE_SZ sizeof(struct llist_node)
+
+/* similar to kmalloc, but sizeof == 8 bucket is gone */
+static u8 size_index[24] __ro_after_init = {
+	3,	/* 8 */
+	3,	/* 16 */
+	4,	/* 24 */
+	4,	/* 32 */
+	5,	/* 40 */
+	5,	/* 48 */
+	5,	/* 56 */
+	5,	/* 64 */
+	1,	/* 72 */
+	1,	/* 80 */
+	1,	/* 88 */
+	1,	/* 96 */
+	6,	/* 104 */
+	6,	/* 112 */
+	6,	/* 120 */
+	6,	/* 128 */
+	2,	/* 136 */
+	2,	/* 144 */
+	2,	/* 152 */
+	2,	/* 160 */
+	2,	/* 168 */
+	2,	/* 176 */
+	2,	/* 184 */
+	2	/* 192 */
+};
+
+static int bpf_mem_cache_idx(size_t size)
+{
+	if (!size || size > 4096)
+		return -1;
+
+	if (size <= 192)
+		return size_index[(size - 1) / 8] - 1;
+
+	return fls(size - 1) - 1;
+}
+
+#define NUM_CACHES 11
+
+struct bpf_mem_cache {
+	/* per-cpu list of free objects of size 'unit_size'.
+	 * All accesses are done with interrupts disabled and 'active' counter
+	 * protection with __llist_add() and __llist_del_first().
+	 */
+	struct llist_head free_llist;
+	local_t active;
+
+	/* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
+	 * are sequenced by per-cpu 'active' counter. But unit_free() cannot
+	 * fail. When 'active' is busy the unit_free() will add an object to
+	 * free_llist_extra.
+	 */
+	struct llist_head free_llist_extra;
+
+	/* kmem_cache != NULL when bpf_mem_alloc was created for specific
+	 * element size.
+	 */
+	struct kmem_cache *kmem_cache;
+	struct irq_work refill_work;
+	struct obj_cgroup *objcg;
+	int unit_size;
+	/* count of objects in free_llist */
+	int free_cnt;
+};
+
+struct bpf_mem_caches {
+	struct bpf_mem_cache cache[NUM_CACHES];
+};
+
+static struct llist_node notrace *__llist_del_first(struct llist_head *head)
+{
+	struct llist_node *entry, *next;
+
+	entry = head->first;
+	if (!entry)
+		return NULL;
+	next = entry->next;
+	head->first = next;
+	return entry;
+}
+
+#define BATCH 48
+#define LOW_WATERMARK 32
+#define HIGH_WATERMARK 96
+/* Assuming the average number of elements per bucket is 64, when all buckets
+ * are used the total memory will be: 64*16*32 + 64*32*32 + 64*64*32 + ... +
+ * 64*4096*32 ~ 20Mbyte
+ */
+
+static void *__alloc(struct bpf_mem_cache *c, int node)
+{
+	/* Allocate, but don't deplete atomic reserves that typical
+	 * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
+	 * will allocate from the current numa node which is what we
+	 * want here.
+	 */
+	gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
+
+	if (c->kmem_cache)
+		return kmem_cache_alloc_node(c->kmem_cache, flags, node);
+
+	return kmalloc_node(c->unit_size, flags, node);
+}
+
+static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
+{
+#ifdef CONFIG_MEMCG_KMEM
+	if (c->objcg)
+		return get_mem_cgroup_from_objcg(c->objcg);
+#endif
+
+#ifdef CONFIG_MEMCG
+	return root_mem_cgroup;
+#else
+	return NULL;
+#endif
+}
+
+/* Mostly runs from irq_work except __init phase. */
+static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
+{
+	struct mem_cgroup *memcg = NULL, *old_memcg;
+	unsigned long flags;
+	void *obj;
+	int i;
+
+	memcg = get_memcg(c);
+	old_memcg = set_active_memcg(memcg);
+	for (i = 0; i < cnt; i++) {
+		obj = __alloc(c, node);
+		if (!obj)
+			break;
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))
+			/* In RT irq_work runs in per-cpu kthread, so disable
+			 * interrupts to avoid preemption and interrupts and
+			 * reduce the chance of bpf prog executing on this cpu
+			 * when active counter is busy.
+			 */
+			local_irq_save(flags);
+		if (local_inc_return(&c->active) == 1) {
+			__llist_add(obj, &c->free_llist);
+			c->free_cnt++;
+		}
+		local_dec(&c->active);
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_restore(flags);
+	}
+	set_active_memcg(old_memcg);
+	mem_cgroup_put(memcg);
+}
+
+static void free_one(struct bpf_mem_cache *c, void *obj)
+{
+	if (c->kmem_cache)
+		kmem_cache_free(c->kmem_cache, obj);
+	else
+		kfree(obj);
+}
+
+static void free_bulk(struct bpf_mem_cache *c)
+{
+	struct llist_node *llnode, *t;
+	unsigned long flags;
+	int cnt;
+
+	do {
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_save(flags);
+		if (local_inc_return(&c->active) == 1) {
+			llnode = __llist_del_first(&c->free_llist);
+			if (llnode)
+				cnt = --c->free_cnt;
+			else
+				cnt = 0;
+		}
+		local_dec(&c->active);
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_restore(flags);
+		free_one(c, llnode);
+	} while (cnt > (HIGH_WATERMARK + LOW_WATERMARK) / 2);
+
+	/* and drain free_llist_extra */
+	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
+		free_one(c, llnode);
+}
+
+static void bpf_mem_refill(struct irq_work *work)
+{
+	struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
+	int cnt;
+
+	/* Racy access to free_cnt. It doesn't need to be 100% accurate */
+	cnt = c->free_cnt;
+	if (cnt < LOW_WATERMARK)
+		/* irq_work runs on this cpu and kmalloc will allocate
+		 * from the current numa node which is what we want here.
+		 */
+		alloc_bulk(c, BATCH, NUMA_NO_NODE);
+	else if (cnt > HIGH_WATERMARK)
+		free_bulk(c);
+}
+
+static void notrace irq_work_raise(struct bpf_mem_cache *c)
+{
+	irq_work_queue(&c->refill_work);
+}
+
+static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
+{
+	init_irq_work(&c->refill_work, bpf_mem_refill);
+	/* To avoid consuming memory assume that 1st run of bpf
+	 * prog won't be doing more than 4 map_update_elem from
+	 * irq disabled region
+	 */
+	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu));
+}
+
+/* When size != 0 create kmem_cache and bpf_mem_cache for each cpu.
+ * This is typical bpf hash map use case when all elements have equal size.
+ *
+ * When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
+ * kmalloc/kfree. Max allocation size is 4096 in this case.
+ * This is bpf_dynptr and bpf_kptr use case.
+ */
+int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
+{
+	static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
+	struct bpf_mem_caches *cc, __percpu *pcc;
+	struct bpf_mem_cache *c, __percpu *pc;
+	struct kmem_cache *kmem_cache;
+	struct obj_cgroup *objcg = NULL;
+	char buf[32];
+	int cpu, i;
+
+	if (size) {
+		pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
+		if (!pc)
+			return -ENOMEM;
+		size += LLIST_NODE_SZ; /* room for llist_node */
+		snprintf(buf, sizeof(buf), "bpf-%u", size);
+		kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
+		if (!kmem_cache) {
+			free_percpu(pc);
+			return -ENOMEM;
+		}
+#ifdef CONFIG_MEMCG_KMEM
+		objcg = get_obj_cgroup_from_current();
+#endif
+		for_each_possible_cpu(cpu) {
+			c = per_cpu_ptr(pc, cpu);
+			c->kmem_cache = kmem_cache;
+			c->unit_size = size;
+			c->objcg = objcg;
+			prefill_mem_cache(c, cpu);
+		}
+		ma->cache = pc;
+		return 0;
+	}
+
+	pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
+	if (!pcc)
+		return -ENOMEM;
+#ifdef CONFIG_MEMCG_KMEM
+	objcg = get_obj_cgroup_from_current();
+#endif
+	for_each_possible_cpu(cpu) {
+		cc = per_cpu_ptr(pcc, cpu);
+		for (i = 0; i < NUM_CACHES; i++) {
+			c = &cc->cache[i];
+			c->unit_size = sizes[i];
+			c->objcg = objcg;
+			prefill_mem_cache(c, cpu);
+		}
+	}
+	ma->caches = pcc;
+	return 0;
+}
+
+static void drain_mem_cache(struct bpf_mem_cache *c)
+{
+	struct llist_node *llnode, *t;
+
+	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
+		free_one(c, llnode);
+	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
+		free_one(c, llnode);
+}
+
+void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
+{
+	struct bpf_mem_caches *cc;
+	struct bpf_mem_cache *c;
+	int cpu, i;
+
+	if (ma->cache) {
+		for_each_possible_cpu(cpu) {
+			c = per_cpu_ptr(ma->cache, cpu);
+			drain_mem_cache(c);
+		}
+		/* kmem_cache and memcg are the same across cpus */
+		kmem_cache_destroy(c->kmem_cache);
+		if (c->objcg)
+			obj_cgroup_put(c->objcg);
+		free_percpu(ma->cache);
+		ma->cache = NULL;
+	}
+	if (ma->caches) {
+		for_each_possible_cpu(cpu) {
+			cc = per_cpu_ptr(ma->caches, cpu);
+			for (i = 0; i < NUM_CACHES; i++) {
+				c = &cc->cache[i];
+				drain_mem_cache(c);
+			}
+		}
+		if (c->objcg)
+			obj_cgroup_put(c->objcg);
+		free_percpu(ma->caches);
+		ma->caches = NULL;
+	}
+}
+
+/* notrace is necessary here and in other functions to make sure
+ * bpf programs cannot attach to them and cause llist corruptions.
+ */
+static void notrace *unit_alloc(struct bpf_mem_cache *c)
+{
+	struct llist_node *llnode = NULL;
+	unsigned long flags;
+	int cnt = 0;
+
+	/* Disable irqs to prevent the following race for majority of prog types:
+	 * prog_A
+	 *   bpf_mem_alloc
+	 *      preemption or irq -> prog_B
+	 *        bpf_mem_alloc
+	 *
+	 * but prog_B could be a perf_event NMI prog.
+	 * Use per-cpu 'active' counter to order free_list access between
+	 * unit_alloc/unit_free/bpf_mem_refill.
+	 */
+	local_irq_save(flags);
+	if (local_inc_return(&c->active) == 1) {
+		llnode = __llist_del_first(&c->free_llist);
+		if (llnode)
+			cnt = --c->free_cnt;
+	}
+	local_dec(&c->active);
+	local_irq_restore(flags);
+
+	WARN_ON(cnt < 0);
+
+	if (cnt < LOW_WATERMARK)
+		irq_work_raise(c);
+	return llnode;
+}
+
+/* Though 'ptr' object could have been allocated on a different cpu
+ * add it to the free_llist of the current cpu.
+ * Let kfree() logic deal with it when it's later called from irq_work.
+ */
+static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
+{
+	struct llist_node *llnode = ptr - LLIST_NODE_SZ;
+	unsigned long flags;
+	int cnt = 0;
+
+	BUILD_BUG_ON(LLIST_NODE_SZ > 8);
+
+	local_irq_save(flags);
+	if (local_inc_return(&c->active) == 1) {
+		__llist_add(llnode, &c->free_llist);
+		cnt = ++c->free_cnt;
+	} else {
+		/* unit_free() cannot fail. Therefore add an object to atomic
+		 * llist. free_bulk() will drain it. Though free_llist_extra is
+		 * a per-cpu list we have to use atomic llist_add here, since
+		 * it also can be interrupted by bpf nmi prog that does another
+		 * unit_free() into the same free_llist_extra.
+		 */
+		llist_add(llnode, &c->free_llist_extra);
+	}
+	local_dec(&c->active);
+	local_irq_restore(flags);
+
+	if (cnt > HIGH_WATERMARK)
+		/* free few objects from current cpu into global kmalloc pool */
+		irq_work_raise(c);
+}
+
+/* Called from BPF program or from sys_bpf syscall.
+ * In both cases migration is disabled.
+ */
+void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
+{
+	int idx;
+	void *ret;
+
+	if (!size)
+		return ZERO_SIZE_PTR;
+
+	idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
+	if (idx < 0)
+		return NULL;
+
+	ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
+	return !ret ? NULL : ret + LLIST_NODE_SZ;
+}
+
+void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
+{
+	int idx;
+
+	if (!ptr)
+		return;
+
+	idx = bpf_mem_cache_idx(__ksize(ptr - LLIST_NODE_SZ));
+	if (idx < 0)
+		return;
+
+	unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
+}
+
+void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
+{
+	void *ret;
+
+	ret = unit_alloc(this_cpu_ptr(ma->cache));
+	return !ret ? NULL : ret + LLIST_NODE_SZ;
+}
+
+void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
+{
+	if (!ptr)
+		return;
+
+	unit_free(this_cpu_ptr(ma->cache), ptr);
+}
-- 
2.30.2

[PATCH v3 bpf-next 02/15] bpf: Convert hash map to bpf_mem_alloc.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Convert bpf hash map to use bpf memory allocator.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/hashtab.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index b301a63afa2f..bd23c8830d49 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -14,6 +14,7 @@
 #include "percpu_freelist.h"
 #include "bpf_lru_list.h"
 #include "map_in_map.h"
+#include <linux/bpf_mem_alloc.h>
 
 #define HTAB_CREATE_FLAG_MASK						\
 	(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE |	\
@@ -92,6 +93,7 @@ struct bucket {
 
 struct bpf_htab {
 	struct bpf_map map;
+	struct bpf_mem_alloc ma;
 	struct bucket *buckets;
 	void *elems;
 	union {
@@ -563,6 +565,10 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 			if (err)
 				goto free_prealloc;
 		}
+	} else {
+		err = bpf_mem_alloc_init(&htab->ma, htab->elem_size);
+		if (err)
+			goto free_map_locked;
 	}
 
 	return &htab->map;
@@ -573,6 +579,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->ma);
 free_htab:
 	lockdep_unregister_key(&htab->lockdep_key);
 	bpf_map_area_free(htab);
@@ -849,7 +856,7 @@ static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)
 	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
 		free_percpu(htab_elem_get_ptr(l, htab->map.key_size));
 	check_and_free_fields(htab, l);
-	kfree(l);
+	bpf_mem_cache_free(&htab->ma, l);
 }
 
 static void htab_elem_free_rcu(struct rcu_head *head)
@@ -973,9 +980,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 				l_new = ERR_PTR(-E2BIG);
 				goto dec_count;
 			}
-		l_new = bpf_map_kmalloc_node(&htab->map, htab->elem_size,
-					     GFP_NOWAIT | __GFP_NOWARN,
-					     htab->map.numa_node);
+		l_new = bpf_mem_cache_alloc(&htab->ma);
 		if (!l_new) {
 			l_new = ERR_PTR(-ENOMEM);
 			goto dec_count;
@@ -994,7 +999,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 			pptr = bpf_map_alloc_percpu(&htab->map, size, 8,
 						    GFP_NOWAIT | __GFP_NOWARN);
 			if (!pptr) {
-				kfree(l_new);
+				bpf_mem_cache_free(&htab->ma, l_new);
 				l_new = ERR_PTR(-ENOMEM);
 				goto dec_count;
 			}
@@ -1489,6 +1494,7 @@ static void htab_map_free(struct bpf_map *map)
 	bpf_map_free_kptr_off_tab(map);
 	free_percpu(htab->extra_elems);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->ma);
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	lockdep_unregister_key(&htab->lockdep_key);
-- 
2.30.2

[PATCH v3 bpf-next 03/15] selftests/bpf: Improve test coverage of test_maps

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Make test_maps more stressful with more parallelism in
update/delete/lookup/walk including different value sizes.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/testing/selftests/bpf/test_maps.c | 38 ++++++++++++++++---------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index cbebfaa7c1e8..d1ffc76814d9 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -264,10 +264,11 @@ static void test_hashmap_percpu(unsigned int task, void *data)
 	close(fd);
 }
 
+#define VALUE_SIZE 3
 static int helper_fill_hashmap(int max_entries)
 {
 	int i, fd, ret;
-	long long key, value;
+	long long key, value[VALUE_SIZE] = {};
 
 	fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(key), sizeof(value),
 			    max_entries, &map_opts);
@@ -276,8 +277,8 @@ static int helper_fill_hashmap(int max_entries)
 	      "err: %s, flags: 0x%x\n", strerror(errno), map_opts.map_flags);
 
 	for (i = 0; i < max_entries; i++) {
-		key = i; value = key;
-		ret = bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST);
+		key = i; value[0] = key;
+		ret = bpf_map_update_elem(fd, &key, value, BPF_NOEXIST);
 		CHECK(ret != 0,
 		      "can't update hashmap",
 		      "err: %s\n", strerror(ret));
@@ -288,8 +289,8 @@ static int helper_fill_hashmap(int max_entries)
 
 static void test_hashmap_walk(unsigned int task, void *data)
 {
-	int fd, i, max_entries = 1000;
-	long long key, value, next_key;
+	int fd, i, max_entries = 10000;
+	long long key, value[VALUE_SIZE], next_key;
 	bool next_key_valid = true;
 
 	fd = helper_fill_hashmap(max_entries);
@@ -297,7 +298,7 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
 					 &next_key) == 0; i++) {
 		key = next_key;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
 	}
 
 	assert(i == max_entries);
@@ -305,9 +306,9 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	assert(bpf_map_get_next_key(fd, NULL, &key) == 0);
 	for (i = 0; next_key_valid; i++) {
 		next_key_valid = bpf_map_get_next_key(fd, &key, &next_key) == 0;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
-		value++;
-		assert(bpf_map_update_elem(fd, &key, &value, BPF_EXIST) == 0);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
+		value[0]++;
+		assert(bpf_map_update_elem(fd, &key, value, BPF_EXIST) == 0);
 		key = next_key;
 	}
 
@@ -316,8 +317,8 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
 					 &next_key) == 0; i++) {
 		key = next_key;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
-		assert(value - 1 == key);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
+		assert(value[0] - 1 == key);
 	}
 
 	assert(i == max_entries);
@@ -1371,16 +1372,16 @@ static void __run_parallel(unsigned int tasks,
 
 static void test_map_stress(void)
 {
+	run_parallel(100, test_hashmap_walk, NULL);
 	run_parallel(100, test_hashmap, NULL);
 	run_parallel(100, test_hashmap_percpu, NULL);
 	run_parallel(100, test_hashmap_sizes, NULL);
-	run_parallel(100, test_hashmap_walk, NULL);
 
 	run_parallel(100, test_arraymap, NULL);
 	run_parallel(100, test_arraymap_percpu, NULL);
 }
 
-#define TASKS 1024
+#define TASKS 100
 
 #define DO_UPDATE 1
 #define DO_DELETE 0
@@ -1432,6 +1433,8 @@ static void test_update_delete(unsigned int fn, void *data)
 	int fd = ((int *)data)[0];
 	int i, key, value, err;
 
+	if (fn & 1)
+		test_hashmap_walk(fn, NULL);
 	for (i = fn; i < MAP_SIZE; i += TASKS) {
 		key = value = i;
 
@@ -1455,7 +1458,7 @@ static void test_update_delete(unsigned int fn, void *data)
 
 static void test_map_parallel(void)
 {
-	int i, fd, key = 0, value = 0;
+	int i, fd, key = 0, value = 0, j = 0;
 	int data[2];
 
 	fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(key), sizeof(value),
@@ -1466,6 +1469,7 @@ static void test_map_parallel(void)
 		exit(1);
 	}
 
+again:
 	/* Use the same fd in children to add elements to this map:
 	 * child_0 adds key=0, key=1024, key=2048, ...
 	 * child_1 adds key=1, key=1025, key=2049, ...
@@ -1502,6 +1506,12 @@ static void test_map_parallel(void)
 	key = -1;
 	assert(bpf_map_get_next_key(fd, NULL, &key) < 0 && errno == ENOENT);
 	assert(bpf_map_get_next_key(fd, &key, &key) < 0 && errno == ENOENT);
+
+	key = 0;
+	bpf_map_delete_elem(fd, &key);
+	if (j++ < 5)
+		goto again;
+	close(fd);
 }
 
 static void test_map_rdonly(void)
-- 
2.30.2

[PATCH v3 bpf-next 04/15] samples/bpf: Reduce syscall overhead in map_perf_test.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Make map_perf_test for preallocated and non-preallocated hash map
spend more time inside bpf program to focus performance analysis
on the speed of update/lookup/delete operations performed by bpf program.

It makes 'perf report' of bpf_mem_alloc look like:
 11.76%  map_perf_test    [k] _raw_spin_lock_irqsave
 11.26%  map_perf_test    [k] htab_map_update_elem
  9.70%  map_perf_test    [k] _raw_spin_lock
  9.47%  map_perf_test    [k] htab_map_delete_elem
  8.57%  map_perf_test    [k] memcpy_erms
  5.58%  map_perf_test    [k] alloc_htab_elem
  4.09%  map_perf_test    [k] __htab_map_lookup_elem
  3.44%  map_perf_test    [k] syscall_exit_to_user_mode
  3.13%  map_perf_test    [k] lookup_nulls_elem_raw
  3.05%  map_perf_test    [k] migrate_enable
  3.04%  map_perf_test    [k] memcmp
  2.67%  map_perf_test    [k] unit_free
  2.39%  map_perf_test    [k] lookup_elem_raw

Reduce default iteration count as well to make 'map_perf_test' quick enough
even on debug kernels.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 samples/bpf/map_perf_test_kern.c | 44 ++++++++++++++++++++------------
 samples/bpf/map_perf_test_user.c |  2 +-
 2 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/samples/bpf/map_perf_test_kern.c b/samples/bpf/map_perf_test_kern.c
index 8773f22b6a98..7342c5b2f278 100644
--- a/samples/bpf/map_perf_test_kern.c
+++ b/samples/bpf/map_perf_test_kern.c
@@ -108,11 +108,14 @@ int stress_hmap(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
-	bpf_map_update_elem(&hash_map, &key, &init_val, BPF_ANY);
-	value = bpf_map_lookup_elem(&hash_map, &key);
-	if (value)
-		bpf_map_delete_elem(&hash_map, &key);
+	for (i = 0; i < 10; i++) {
+		bpf_map_update_elem(&hash_map, &key, &init_val, BPF_ANY);
+		value = bpf_map_lookup_elem(&hash_map, &key);
+		if (value)
+			bpf_map_delete_elem(&hash_map, &key);
+	}
 
 	return 0;
 }
@@ -123,11 +126,14 @@ int stress_percpu_hmap(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
-	bpf_map_update_elem(&percpu_hash_map, &key, &init_val, BPF_ANY);
-	value = bpf_map_lookup_elem(&percpu_hash_map, &key);
-	if (value)
-		bpf_map_delete_elem(&percpu_hash_map, &key);
+	for (i = 0; i < 10; i++) {
+		bpf_map_update_elem(&percpu_hash_map, &key, &init_val, BPF_ANY);
+		value = bpf_map_lookup_elem(&percpu_hash_map, &key);
+		if (value)
+			bpf_map_delete_elem(&percpu_hash_map, &key);
+	}
 	return 0;
 }
 
@@ -137,11 +143,14 @@ int stress_hmap_alloc(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
-	bpf_map_update_elem(&hash_map_alloc, &key, &init_val, BPF_ANY);
-	value = bpf_map_lookup_elem(&hash_map_alloc, &key);
-	if (value)
-		bpf_map_delete_elem(&hash_map_alloc, &key);
+	for (i = 0; i < 10; i++) {
+		bpf_map_update_elem(&hash_map_alloc, &key, &init_val, BPF_ANY);
+		value = bpf_map_lookup_elem(&hash_map_alloc, &key);
+		if (value)
+			bpf_map_delete_elem(&hash_map_alloc, &key);
+	}
 	return 0;
 }
 
@@ -151,11 +160,14 @@ int stress_percpu_hmap_alloc(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
-	bpf_map_update_elem(&percpu_hash_map_alloc, &key, &init_val, BPF_ANY);
-	value = bpf_map_lookup_elem(&percpu_hash_map_alloc, &key);
-	if (value)
-		bpf_map_delete_elem(&percpu_hash_map_alloc, &key);
+	for (i = 0; i < 10; i++) {
+		bpf_map_update_elem(&percpu_hash_map_alloc, &key, &init_val, BPF_ANY);
+		value = bpf_map_lookup_elem(&percpu_hash_map_alloc, &key);
+		if (value)
+			bpf_map_delete_elem(&percpu_hash_map_alloc, &key);
+	}
 	return 0;
 }
 
diff --git a/samples/bpf/map_perf_test_user.c b/samples/bpf/map_perf_test_user.c
index b6fc174ab1f2..1bb53f4b29e1 100644
--- a/samples/bpf/map_perf_test_user.c
+++ b/samples/bpf/map_perf_test_user.c
@@ -72,7 +72,7 @@ static int test_flags = ~0;
 static uint32_t num_map_entries;
 static uint32_t inner_lru_hash_size;
 static int lru_hash_lookup_test_entries = 32;
-static uint32_t max_cnt = 1000000;
+static uint32_t max_cnt = 10000;
 
 static int check_test_flags(enum test_type t)
 {
-- 
2.30.2

[PATCH v3 bpf-next 05/15] bpf: Relax the requirement to use preallocated hash maps in tracing progs.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Since bpf hash map was converted to use bpf_mem_alloc it is safe to use
from tracing programs and in RT kernels.
But per-cpu hash map is still using dynamic allocation for per-cpu map
values, hence keep the warning for this map type.
In the future alloc_percpu_gfp can be front-end-ed with bpf_mem_cache
and this restriction will be completely lifted.
perf_event (NMI) bpf programs have to use preallocated hash maps,
because free_htab_elem() is using call_rcu which might crash if re-entered.

Sleepable bpf programs have to use preallocated hash maps, because
life time of the map elements is not protected by rcu_read_lock/unlock.
This restriction can be lifted in the future as well.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2c1f8069f7b7..d785f29047d7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12605,10 +12605,12 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 	 * For programs attached to PERF events this is mandatory as the
 	 * perf NMI can hit any arbitrary code sequence.
 	 *
-	 * All other trace types using preallocated hash maps are unsafe as
-	 * well because tracepoint or kprobes can be inside locked regions
-	 * of the memory allocator or at a place where a recursion into the
-	 * memory allocator would see inconsistent state.
+	 * All other trace types using non-preallocated per-cpu hash maps are
+	 * unsafe as well because tracepoint or kprobes can be inside locked
+	 * regions of the per-cpu memory allocator or at a place where a
+	 * recursion into the per-cpu memory allocator would see inconsistent
+	 * state. Non per-cpu hash maps are using bpf_mem_alloc-tor which is
+	 * safe to use from kprobe/fentry and in RT.
 	 *
 	 * On RT enabled kernels run-time allocation of all trace type
 	 * programs is strictly prohibited due to lock type constraints. On
@@ -12618,15 +12620,26 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 	 */
 	if (is_tracing_prog_type(prog_type) && !is_preallocated_map(map)) {
 		if (prog_type == BPF_PROG_TYPE_PERF_EVENT) {
+			/* perf_event bpf progs have to use preallocated hash maps
+			 * because non-prealloc is still relying on call_rcu to free
+			 * elements.
+			 */
 			verbose(env, "perf_event programs can only use preallocated hash map\n");
 			return -EINVAL;
 		}
-		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
-			verbose(env, "trace type programs can only use preallocated hash map\n");
-			return -EINVAL;
+		if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+		    (map->inner_map_meta &&
+		     map->inner_map_meta->map_type == BPF_MAP_TYPE_PERCPU_HASH)) {
+			if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+				verbose(env,
+					"trace type programs can only use preallocated per-cpu hash map\n");
+				return -EINVAL;
+			}
+			WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
+			verbose(env,
+				"trace type programs with run-time allocated per-cpu hash maps are unsafe."
+				" Switch to preallocated hash maps.\n");
 		}
-		WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
-		verbose(env, "trace type programs with run-time allocated hash maps are unsafe. Switch to preallocated hash maps.\n");
 	}
 
 	if (map_value_has_spin_lock(map)) {
-- 
2.30.2

[PATCH v3 bpf-next 06/15] bpf: Optimize element count in non-preallocated hash map.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

The atomic_inc/dec might cause extreme cache line bouncing when multiple cpus
access the same bpf map. Based on specified max_entries for the hash map
calculate when percpu_counter becomes faster than atomic_t and use it for such
maps. For example samples/bpf/map_perf_test is using hash map with max_entries
1000. On a system with 16 cpus the 'map_perf_test 4' shows 14k events per
second using atomic_t. On a system with 15 cpus it shows 100k events per second
using percpu. map_perf_test is an extreme case where all cpus colliding on
atomic_t which causes extreme cache bouncing. Note that the slow path of
percpu_counter is 5k events per secound vs 14k for atomic, so the heuristic is
necessary. See comment in the code why the heuristic is based on
num_online_cpus().

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/hashtab.c | 70 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 62 insertions(+), 8 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index bd23c8830d49..8f68c6e13339 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -101,7 +101,12 @@ struct bpf_htab {
 		struct bpf_lru lru;
 	};
 	struct htab_elem *__percpu *extra_elems;
-	atomic_t count;	/* number of elements in this hashtable */
+	/* number of elements in non-preallocated hashtable are kept
+	 * in either pcount or count
+	 */
+	struct percpu_counter pcount;
+	atomic_t count;
+	bool use_percpu_counter;
 	u32 n_buckets;	/* number of hash buckets */
 	u32 elem_size;	/* size of each element in bytes */
 	u32 hashrnd;
@@ -552,6 +557,29 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 
 	htab_init_buckets(htab);
 
+/* compute_batch_value() computes batch value as num_online_cpus() * 2
+ * and __percpu_counter_compare() needs
+ * htab->max_entries - cur_number_of_elems to be more than batch * num_online_cpus()
+ * for percpu_counter to be faster than atomic_t. In practice the average bpf
+ * hash map size is 10k, which means that a system with 64 cpus will fill
+ * hashmap to 20% of 10k before percpu_counter becomes ineffective. Therefore
+ * define our own batch count as 32 then 10k hash map can be filled up to 80%:
+ * 10k - 8k > 32 _batch_ * 64 _cpus_
+ * and __percpu_counter_compare() will still be fast. At that point hash map
+ * collisions will dominate its performance anyway. Assume that hash map filled
+ * to 50+% isn't going to be O(1) and use the following formula to choose
+ * between percpu_counter and atomic_t.
+ */
+#define PERCPU_COUNTER_BATCH 32
+	if (attr->max_entries / 2 > num_online_cpus() * PERCPU_COUNTER_BATCH)
+		htab->use_percpu_counter = true;
+
+	if (htab->use_percpu_counter) {
+		err = percpu_counter_init(&htab->pcount, 0, GFP_KERNEL);
+		if (err)
+			goto free_map_locked;
+	}
+
 	if (prealloc) {
 		err = prealloc_init(htab);
 		if (err)
@@ -878,6 +906,31 @@ static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
 	}
 }
 
+static bool is_map_full(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		return __percpu_counter_compare(&htab->pcount, htab->map.max_entries,
+						PERCPU_COUNTER_BATCH) >= 0;
+	return atomic_read(&htab->count) >= htab->map.max_entries;
+}
+
+static void inc_elem_count(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		percpu_counter_add_batch(&htab->pcount, 1, PERCPU_COUNTER_BATCH);
+	else
+		atomic_inc(&htab->count);
+}
+
+static void dec_elem_count(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		percpu_counter_add_batch(&htab->pcount, -1, PERCPU_COUNTER_BATCH);
+	else
+		atomic_dec(&htab->count);
+}
+
+
 static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 {
 	htab_put_fd_value(htab, l);
@@ -886,7 +939,7 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 		check_and_free_fields(htab, l);
 		__pcpu_freelist_push(&htab->freelist, &l->fnode);
 	} else {
-		atomic_dec(&htab->count);
+		dec_elem_count(htab);
 		l->htab = htab;
 		call_rcu(&l->rcu, htab_elem_free_rcu);
 	}
@@ -970,16 +1023,15 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 			l_new = container_of(l, struct htab_elem, fnode);
 		}
 	} else {
-		if (atomic_inc_return(&htab->count) > htab->map.max_entries)
-			if (!old_elem) {
+		if (is_map_full(htab))
+			if (!old_elem)
 				/* when map is full and update() is replacing
 				 * old element, it's ok to allocate, since
 				 * old element will be freed immediately.
 				 * Otherwise return an error
 				 */
-				l_new = ERR_PTR(-E2BIG);
-				goto dec_count;
-			}
+				return ERR_PTR(-E2BIG);
+		inc_elem_count(htab);
 		l_new = bpf_mem_cache_alloc(&htab->ma);
 		if (!l_new) {
 			l_new = ERR_PTR(-ENOMEM);
@@ -1021,7 +1073,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 	l_new->hash = hash;
 	return l_new;
 dec_count:
-	atomic_dec(&htab->count);
+	dec_elem_count(htab);
 	return l_new;
 }
 
@@ -1495,6 +1547,8 @@ static void htab_map_free(struct bpf_map *map)
 	free_percpu(htab->extra_elems);
 	bpf_map_area_free(htab->buckets);
 	bpf_mem_alloc_destroy(&htab->ma);
+	if (htab->use_percpu_counter)
+		percpu_counter_destroy(&htab->pcount);
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	lockdep_unregister_key(&htab->lockdep_key);
-- 
2.30.2

[PATCH v3 bpf-next 07/15] bpf: Optimize call_rcu in non-preallocated hash map.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Doing call_rcu() million times a second becomes a bottle neck.
Convert non-preallocated hash map from call_rcu to SLAB_TYPESAFE_BY_RCU.
The rcu critical section is no longer observed for one htab element
which makes non-preallocated hash map behave just like preallocated hash map.
The map elements are released back to kernel memory after observing
rcu critical section.
This improves 'map_perf_test 4' performance from 100k events per second
to 250k events per second.

bpf_mem_alloc + percpu_counter + typesafe_by_rcu provide 10x performance
boost to non-preallocated hash map and make it within few % of preallocated map
while consuming fraction of memory.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/hashtab.c                      |  8 ++++++--
 kernel/bpf/memalloc.c                     |  2 +-
 tools/testing/selftests/bpf/progs/timer.c | 11 -----------
 3 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 8f68c6e13339..299ab98f9811 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -940,8 +940,12 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 		__pcpu_freelist_push(&htab->freelist, &l->fnode);
 	} else {
 		dec_elem_count(htab);
-		l->htab = htab;
-		call_rcu(&l->rcu, htab_elem_free_rcu);
+		if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH) {
+			l->htab = htab;
+			call_rcu(&l->rcu, htab_elem_free_rcu);
+		} else {
+			htab_elem_free(htab, l);
+		}
 	}
 }
 
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 293380eaea41..cfa07f539eda 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -276,7 +276,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
 			return -ENOMEM;
 		size += LLIST_NODE_SZ; /* room for llist_node */
 		snprintf(buf, sizeof(buf), "bpf-%u", size);
-		kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
+		kmem_cache = kmem_cache_create(buf, size, 8, SLAB_TYPESAFE_BY_RCU, NULL);
 		if (!kmem_cache) {
 			free_percpu(pc);
 			return -ENOMEM;
diff --git a/tools/testing/selftests/bpf/progs/timer.c b/tools/testing/selftests/bpf/progs/timer.c
index 5f5309791649..0053c5402173 100644
--- a/tools/testing/selftests/bpf/progs/timer.c
+++ b/tools/testing/selftests/bpf/progs/timer.c
@@ -208,17 +208,6 @@ static int timer_cb2(void *map, int *key, struct hmap_elem *val)
 		 */
 		bpf_map_delete_elem(map, key);
 
-		/* in non-preallocated hashmap both 'key' and 'val' are RCU
-		 * protected and still valid though this element was deleted
-		 * from the map. Arm this timer for ~35 seconds. When callback
-		 * finishes the call_rcu will invoke:
-		 * htab_elem_free_rcu
-		 *   check_and_free_timer
-		 *     bpf_timer_cancel_and_free
-		 * to cancel this 35 second sleep and delete the timer for real.
-		 */
-		if (bpf_timer_start(&val->timer, 1ull << 35, 0) != 0)
-			err |= 256;
 		ok |= 4;
 	}
 	return 0;
-- 
2.30.2

[PATCH v3 bpf-next 08/15] bpf: Adjust low/high watermarks in bpf_mem_cache

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

The same low/high watermarks for every bucket in bpf_mem_cache consume
significant amount of memory. Preallocating 64 elements of 4096 bytes each in
the free list is not efficient. Make low/high watermarks and batching value
dependent on element size. This change brings significant memory savings.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/memalloc.c | 50 +++++++++++++++++++++++++++++++------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index cfa07f539eda..22b729914afe 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -99,6 +99,7 @@ struct bpf_mem_cache {
 	int unit_size;
 	/* count of objects in free_llist */
 	int free_cnt;
+	int low_watermark, high_watermark, batch;
 };
 
 struct bpf_mem_caches {
@@ -117,14 +118,6 @@ static struct llist_node notrace *__llist_del_first(struct llist_head *head)
 	return entry;
 }
 
-#define BATCH 48
-#define LOW_WATERMARK 32
-#define HIGH_WATERMARK 96
-/* Assuming the average number of elements per bucket is 64, when all buckets
- * are used the total memory will be: 64*16*32 + 64*32*32 + 64*64*32 + ... +
- * 64*4096*32 ~ 20Mbyte
- */
-
 static void *__alloc(struct bpf_mem_cache *c, int node)
 {
 	/* Allocate, but don't deplete atomic reserves that typical
@@ -215,7 +208,7 @@ static void free_bulk(struct bpf_mem_cache *c)
 		if (IS_ENABLED(CONFIG_PREEMPT_RT))
 			local_irq_restore(flags);
 		free_one(c, llnode);
-	} while (cnt > (HIGH_WATERMARK + LOW_WATERMARK) / 2);
+	} while (cnt > (c->high_watermark + c->low_watermark) / 2);
 
 	/* and drain free_llist_extra */
 	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
@@ -229,12 +222,12 @@ static void bpf_mem_refill(struct irq_work *work)
 
 	/* Racy access to free_cnt. It doesn't need to be 100% accurate */
 	cnt = c->free_cnt;
-	if (cnt < LOW_WATERMARK)
+	if (cnt < c->low_watermark)
 		/* irq_work runs on this cpu and kmalloc will allocate
 		 * from the current numa node which is what we want here.
 		 */
-		alloc_bulk(c, BATCH, NUMA_NO_NODE);
-	else if (cnt > HIGH_WATERMARK)
+		alloc_bulk(c, c->batch, NUMA_NO_NODE);
+	else if (cnt > c->high_watermark)
 		free_bulk(c);
 }
 
@@ -243,9 +236,38 @@ static void notrace irq_work_raise(struct bpf_mem_cache *c)
 	irq_work_queue(&c->refill_work);
 }
 
+/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
+ * the freelist cache will be elem_size * 64 (or less) on each cpu.
+ *
+ * For bpf programs that don't have statically known allocation sizes and
+ * assuming (low_mark + high_mark) / 2 as an average number of elements per
+ * bucket and all buckets are used the total amount of memory in freelists
+ * on each cpu will be:
+ * 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
+ * == ~ 116 Kbyte using below heuristic.
+ * Initialized, but unused bpf allocator (not bpf map specific one) will
+ * consume ~ 11 Kbyte per cpu.
+ * Typical case will be between 11K and 116K closer to 11K.
+ * bpf progs can and should share bpf_mem_cache when possible.
+ */
+
 static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
 {
 	init_irq_work(&c->refill_work, bpf_mem_refill);
+	if (c->unit_size <= 256) {
+		c->low_watermark = 32;
+		c->high_watermark = 96;
+	} else {
+		/* When page_size == 4k, order-0 cache will have low_mark == 2
+		 * and high_mark == 6 with batch alloc of 3 individual pages at
+		 * a time.
+		 * 8k allocs and above low == 1, high == 3, batch == 1.
+		 */
+		c->low_watermark = max(32 * 256 / c->unit_size, 1);
+		c->high_watermark = max(96 * 256 / c->unit_size, 3);
+	}
+	c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
+
 	/* To avoid consuming memory assume that 1st run of bpf
 	 * prog won't be doing more than 4 map_update_elem from
 	 * irq disabled region
@@ -387,7 +409,7 @@ static void notrace *unit_alloc(struct bpf_mem_cache *c)
 
 	WARN_ON(cnt < 0);
 
-	if (cnt < LOW_WATERMARK)
+	if (cnt < c->low_watermark)
 		irq_work_raise(c);
 	return llnode;
 }
@@ -420,7 +442,7 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
 	local_dec(&c->active);
 	local_irq_restore(flags);
 
-	if (cnt > HIGH_WATERMARK)
+	if (cnt > c->high_watermark)
 		/* free few objects from current cpu into global kmalloc pool */
 		irq_work_raise(c);
 }
-- 
2.30.2

[PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
solves the memory consumption issue, avoids kmem_cache_destroy latency and
keeps bpf hash map performance the same.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/memalloc.c | 64 +++++++++++++++++++++++++++++++++++++++++--
 kernel/bpf/syscall.c  |  5 +++-
 2 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 22b729914afe..d765a5cb24b4 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -100,6 +100,11 @@ struct bpf_mem_cache {
 	/* count of objects in free_llist */
 	int free_cnt;
 	int low_watermark, high_watermark, batch;
+
+	struct rcu_head rcu;
+	struct llist_head free_by_rcu;
+	struct llist_head waiting_for_gp;
+	atomic_t call_rcu_in_progress;
 };
 
 struct bpf_mem_caches {
@@ -188,6 +193,45 @@ static void free_one(struct bpf_mem_cache *c, void *obj)
 		kfree(obj);
 }
 
+static void __free_rcu(struct rcu_head *head)
+{
+	struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
+	struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
+	struct llist_node *pos, *t;
+
+	llist_for_each_safe(pos, t, llnode)
+		free_one(c, pos);
+	atomic_set(&c->call_rcu_in_progress, 0);
+}
+
+static void enque_to_free(struct bpf_mem_cache *c, void *obj)
+{
+	struct llist_node *llnode = obj;
+
+	/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
+	 * Nothing races to add to free_by_rcu list.
+	 */
+	__llist_add(llnode, &c->free_by_rcu);
+}
+
+static void do_call_rcu(struct bpf_mem_cache *c)
+{
+	struct llist_node *llnode, *t;
+
+	if (atomic_xchg(&c->call_rcu_in_progress, 1))
+		return;
+
+	WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
+	llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
+		/* There is no concurrent __llist_add(waiting_for_gp) access.
+		 * It doesn't race with llist_del_all either.
+		 * But there could be two concurrent llist_del_all(waiting_for_gp):
+		 * from __free_rcu() and from drain_mem_cache().
+		 */
+		__llist_add(llnode, &c->waiting_for_gp);
+	call_rcu(&c->rcu, __free_rcu);
+}
+
 static void free_bulk(struct bpf_mem_cache *c)
 {
 	struct llist_node *llnode, *t;
@@ -207,12 +251,13 @@ static void free_bulk(struct bpf_mem_cache *c)
 		local_dec(&c->active);
 		if (IS_ENABLED(CONFIG_PREEMPT_RT))
 			local_irq_restore(flags);
-		free_one(c, llnode);
+		enque_to_free(c, llnode);
 	} while (cnt > (c->high_watermark + c->low_watermark) / 2);
 
 	/* and drain free_llist_extra */
 	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
-		free_one(c, llnode);
+		enque_to_free(c, llnode);
+	do_call_rcu(c);
 }
 
 static void bpf_mem_refill(struct irq_work *work)
@@ -298,7 +343,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
 			return -ENOMEM;
 		size += LLIST_NODE_SZ; /* room for llist_node */
 		snprintf(buf, sizeof(buf), "bpf-%u", size);
-		kmem_cache = kmem_cache_create(buf, size, 8, SLAB_TYPESAFE_BY_RCU, NULL);
+		kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
 		if (!kmem_cache) {
 			free_percpu(pc);
 			return -ENOMEM;
@@ -340,6 +385,15 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
 {
 	struct llist_node *llnode, *t;
 
+	/* The caller has done rcu_barrier() and no progs are using this
+	 * bpf_mem_cache, but htab_map_free() called bpf_mem_cache_free() for
+	 * all remaining elements and they can be in free_by_rcu or in
+	 * waiting_for_gp lists, so drain those lists now.
+	 */
+	llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
+		free_one(c, llnode);
+	llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
+		free_one(c, llnode);
 	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
 		free_one(c, llnode);
 	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
@@ -361,6 +415,10 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 		kmem_cache_destroy(c->kmem_cache);
 		if (c->objcg)
 			obj_cgroup_put(c->objcg);
+		/* c->waiting_for_gp list was drained, but __free_rcu might
+		 * still execute. Wait for it now before we free 'c'.
+		 */
+		rcu_barrier();
 		free_percpu(ma->cache);
 		ma->cache = NULL;
 	}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a4d40d98428a..850270a72350 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -638,7 +638,10 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
 		bpf_map_free_id(map, do_idr_lock);
 		btf_put(map->btf);
 		INIT_WORK(&map->work, bpf_map_free_deferred);
-		schedule_work(&map->work);
+		/* Avoid spawning kworkers, since they all might contend
+		 * for the same mutex like slab_mutex.
+		 */
+		queue_work(system_unbound_wq, &map->work);
 	}
 }
 
-- 
2.30.2

[PATCH v3 bpf-next 10/15] bpf: Add percpu allocation support to bpf_mem_alloc.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Extend bpf_mem_alloc to cache free list of fixed size per-cpu allocations.
Once such cache is created bpf_mem_cache_alloc() will return per-cpu objects.
bpf_mem_cache_free() will free them back into global per-cpu pool after
observing RCU grace period.
per-cpu flavor of bpf_mem_alloc is going to be used by per-cpu hash maps.

The free list cache consists of tuples { llist_node, per-cpu pointer }
Unlike alloc_percpu() that returns per-cpu pointer
the bpf_mem_cache_alloc() returns a pointer to per-cpu pointer and
bpf_mem_cache_free() expects to receive it back.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/bpf_mem_alloc.h |  2 +-
 kernel/bpf/hashtab.c          |  2 +-
 kernel/bpf/memalloc.c         | 44 +++++++++++++++++++++++++++++++----
 3 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index 804733070f8d..653ed1584a03 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -12,7 +12,7 @@ struct bpf_mem_alloc {
 	struct bpf_mem_cache __percpu *cache;
 };
 
-int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size);
+int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu);
 void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
 
 /* kmalloc/kfree equivalent: */
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 299ab98f9811..8daa1132d43c 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -594,7 +594,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 				goto free_prealloc;
 		}
 	} else {
-		err = bpf_mem_alloc_init(&htab->ma, htab->elem_size);
+		err = bpf_mem_alloc_init(&htab->ma, htab->elem_size, false);
 		if (err)
 			goto free_map_locked;
 	}
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index d765a5cb24b4..9e5ad7dc4dc7 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -100,6 +100,7 @@ struct bpf_mem_cache {
 	/* count of objects in free_llist */
 	int free_cnt;
 	int low_watermark, high_watermark, batch;
+	bool percpu;
 
 	struct rcu_head rcu;
 	struct llist_head free_by_rcu;
@@ -132,6 +133,19 @@ static void *__alloc(struct bpf_mem_cache *c, int node)
 	 */
 	gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
 
+	if (c->percpu) {
+		void **obj = kmem_cache_alloc_node(c->kmem_cache, flags, node);
+		void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
+
+		if (!obj || !pptr) {
+			free_percpu(pptr);
+			kfree(obj);
+			return NULL;
+		}
+		obj[1] = pptr;
+		return obj;
+	}
+
 	if (c->kmem_cache)
 		return kmem_cache_alloc_node(c->kmem_cache, flags, node);
 
@@ -187,6 +201,12 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
 
 static void free_one(struct bpf_mem_cache *c, void *obj)
 {
+	if (c->percpu) {
+		free_percpu(((void **)obj)[1]);
+		kmem_cache_free(c->kmem_cache, obj);
+		return;
+	}
+
 	if (c->kmem_cache)
 		kmem_cache_free(c->kmem_cache, obj);
 	else
@@ -327,21 +347,30 @@ static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
  * kmalloc/kfree. Max allocation size is 4096 in this case.
  * This is bpf_dynptr and bpf_kptr use case.
  */
-int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
+int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 {
 	static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
 	struct bpf_mem_caches *cc, __percpu *pcc;
 	struct bpf_mem_cache *c, __percpu *pc;
-	struct kmem_cache *kmem_cache;
+	struct kmem_cache *kmem_cache = NULL;
 	struct obj_cgroup *objcg = NULL;
 	char buf[32];
-	int cpu, i;
+	int cpu, i, unit_size;
 
 	if (size) {
 		pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
 		if (!pc)
 			return -ENOMEM;
-		size += LLIST_NODE_SZ; /* room for llist_node */
+
+		if (percpu) {
+			unit_size = size;
+			/* room for llist_node and per-cpu pointer */
+			size = LLIST_NODE_SZ + sizeof(void *);
+		} else {
+			size += LLIST_NODE_SZ; /* room for llist_node */
+			unit_size = size;
+		}
+
 		snprintf(buf, sizeof(buf), "bpf-%u", size);
 		kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
 		if (!kmem_cache) {
@@ -354,14 +383,19 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
 		for_each_possible_cpu(cpu) {
 			c = per_cpu_ptr(pc, cpu);
 			c->kmem_cache = kmem_cache;
-			c->unit_size = size;
+			c->unit_size = unit_size;
 			c->objcg = objcg;
+			c->percpu = percpu;
 			prefill_mem_cache(c, cpu);
 		}
 		ma->cache = pc;
 		return 0;
 	}
 
+	/* size == 0 && percpu is an invalid combination */
+	if (WARN_ON_ONCE(percpu))
+		return -EINVAL;
+
 	pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
 	if (!pcc)
 		return -ENOMEM;
-- 
2.30.2

[PATCH v3 bpf-next 11/15] bpf: Convert percpu hash map to per-cpu bpf_mem_alloc.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Convert dynamic allocations in percpu hash map from alloc_percpu() to
bpf_mem_cache_alloc() from per-cpu bpf_mem_alloc. Since bpf_mem_alloc frees
objects after RCU gp the call_rcu() is removed. pcpu_init_value() now needs to
zero-fill per-cpu allocations, since dynamically allocated map elements are now
similar to full prealloc, since alloc_percpu() is not called inline and the
elements are reused in the freelist.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/hashtab.c | 45 +++++++++++++++++++-------------------------
 1 file changed, 19 insertions(+), 26 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 8daa1132d43c..89f26cbddef5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -94,6 +94,7 @@ struct bucket {
 struct bpf_htab {
 	struct bpf_map map;
 	struct bpf_mem_alloc ma;
+	struct bpf_mem_alloc pcpu_ma;
 	struct bucket *buckets;
 	void *elems;
 	union {
@@ -121,14 +122,14 @@ struct htab_elem {
 		struct {
 			void *padding;
 			union {
-				struct bpf_htab *htab;
 				struct pcpu_freelist_node fnode;
 				struct htab_elem *batch_flink;
 			};
 		};
 	};
 	union {
-		struct rcu_head rcu;
+		/* pointer to per-cpu pointer */
+		void *ptr_to_pptr;
 		struct bpf_lru_node lru_node;
 	};
 	u32 hash;
@@ -435,8 +436,6 @@ static int htab_map_alloc_check(union bpf_attr *attr)
 	bool zero_seed = (attr->map_flags & BPF_F_ZERO_SEED);
 	int numa_node = bpf_map_attr_numa_node(attr);
 
-	BUILD_BUG_ON(offsetof(struct htab_elem, htab) !=
-		     offsetof(struct htab_elem, hash_node.pprev));
 	BUILD_BUG_ON(offsetof(struct htab_elem, fnode.next) !=
 		     offsetof(struct htab_elem, hash_node.pprev));
 
@@ -597,6 +596,12 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 		err = bpf_mem_alloc_init(&htab->ma, htab->elem_size, false);
 		if (err)
 			goto free_map_locked;
+		if (percpu) {
+			err = bpf_mem_alloc_init(&htab->pcpu_ma,
+						 round_up(htab->map.value_size, 8), true);
+			if (err)
+				goto free_map_locked;
+		}
 	}
 
 	return &htab->map;
@@ -607,6 +612,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->pcpu_ma);
 	bpf_mem_alloc_destroy(&htab->ma);
 free_htab:
 	lockdep_unregister_key(&htab->lockdep_key);
@@ -882,19 +888,11 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
 static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)
 {
 	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
-		free_percpu(htab_elem_get_ptr(l, htab->map.key_size));
+		bpf_mem_cache_free(&htab->pcpu_ma, l->ptr_to_pptr);
 	check_and_free_fields(htab, l);
 	bpf_mem_cache_free(&htab->ma, l);
 }
 
-static void htab_elem_free_rcu(struct rcu_head *head)
-{
-	struct htab_elem *l = container_of(head, struct htab_elem, rcu);
-	struct bpf_htab *htab = l->htab;
-
-	htab_elem_free(htab, l);
-}
-
 static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
 {
 	struct bpf_map *map = &htab->map;
@@ -940,12 +938,7 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 		__pcpu_freelist_push(&htab->freelist, &l->fnode);
 	} else {
 		dec_elem_count(htab);
-		if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH) {
-			l->htab = htab;
-			call_rcu(&l->rcu, htab_elem_free_rcu);
-		} else {
-			htab_elem_free(htab, l);
-		}
+		htab_elem_free(htab, l);
 	}
 }
 
@@ -970,13 +963,12 @@ static void pcpu_copy_value(struct bpf_htab *htab, void __percpu *pptr,
 static void pcpu_init_value(struct bpf_htab *htab, void __percpu *pptr,
 			    void *value, bool onallcpus)
 {
-	/* When using prealloc and not setting the initial value on all cpus,
-	 * zero-fill element values for other cpus (just as what happens when
-	 * not using prealloc). Otherwise, bpf program has no way to ensure
+	/* When not setting the initial value on all cpus, zero-fill element
+	 * values for other cpus. Otherwise, bpf program has no way to ensure
 	 * known initial values for cpus other than current one
 	 * (onallcpus=false always when coming from bpf prog).
 	 */
-	if (htab_is_prealloc(htab) && !onallcpus) {
+	if (!onallcpus) {
 		u32 size = round_up(htab->map.value_size, 8);
 		int current_cpu = raw_smp_processor_id();
 		int cpu;
@@ -1047,18 +1039,18 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 
 	memcpy(l_new->key, key, key_size);
 	if (percpu) {
-		size = round_up(size, 8);
 		if (prealloc) {
 			pptr = htab_elem_get_ptr(l_new, key_size);
 		} else {
 			/* alloc_percpu zero-fills */
-			pptr = bpf_map_alloc_percpu(&htab->map, size, 8,
-						    GFP_NOWAIT | __GFP_NOWARN);
+			pptr = bpf_mem_cache_alloc(&htab->pcpu_ma);
 			if (!pptr) {
 				bpf_mem_cache_free(&htab->ma, l_new);
 				l_new = ERR_PTR(-ENOMEM);
 				goto dec_count;
 			}
+			l_new->ptr_to_pptr = pptr;
+			pptr = *(void **)pptr;
 		}
 
 		pcpu_init_value(htab, pptr, value, onallcpus);
@@ -1550,6 +1542,7 @@ static void htab_map_free(struct bpf_map *map)
 	bpf_map_free_kptr_off_tab(map);
 	free_percpu(htab->extra_elems);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->pcpu_ma);
 	bpf_mem_alloc_destroy(&htab->ma);
 	if (htab->use_percpu_counter)
 		percpu_counter_destroy(&htab->pcount);
-- 
2.30.2

[PATCH v3 bpf-next 12/15] bpf: Remove tracing program restriction on map types

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

The hash map is now fully converted to bpf_mem_alloc. Its implementation is not
allocating synchronously and not calling call_rcu() directly. It's now safe to
use non-preallocated hash maps in all types of tracing programs including
BPF_PROG_TYPE_PERF_EVENT that runs out of NMI context.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 42 ------------------------------------------
 1 file changed, 42 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d785f29047d7..a1ada707c57c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12599,48 +12599,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(prog);
-	/*
-	 * Validate that trace type programs use preallocated hash maps.
-	 *
-	 * For programs attached to PERF events this is mandatory as the
-	 * perf NMI can hit any arbitrary code sequence.
-	 *
-	 * All other trace types using non-preallocated per-cpu hash maps are
-	 * unsafe as well because tracepoint or kprobes can be inside locked
-	 * regions of the per-cpu memory allocator or at a place where a
-	 * recursion into the per-cpu memory allocator would see inconsistent
-	 * state. Non per-cpu hash maps are using bpf_mem_alloc-tor which is
-	 * safe to use from kprobe/fentry and in RT.
-	 *
-	 * On RT enabled kernels run-time allocation of all trace type
-	 * programs is strictly prohibited due to lock type constraints. On
-	 * !RT kernels it is allowed for backwards compatibility reasons for
-	 * now, but warnings are emitted so developers are made aware of
-	 * the unsafety and can fix their programs before this is enforced.
-	 */
-	if (is_tracing_prog_type(prog_type) && !is_preallocated_map(map)) {
-		if (prog_type == BPF_PROG_TYPE_PERF_EVENT) {
-			/* perf_event bpf progs have to use preallocated hash maps
-			 * because non-prealloc is still relying on call_rcu to free
-			 * elements.
-			 */
-			verbose(env, "perf_event programs can only use preallocated hash map\n");
-			return -EINVAL;
-		}
-		if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
-		    (map->inner_map_meta &&
-		     map->inner_map_meta->map_type == BPF_MAP_TYPE_PERCPU_HASH)) {
-			if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
-				verbose(env,
-					"trace type programs can only use preallocated per-cpu hash map\n");
-				return -EINVAL;
-			}
-			WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
-			verbose(env,
-				"trace type programs with run-time allocated per-cpu hash maps are unsafe."
-				" Switch to preallocated hash maps.\n");
-		}
-	}
 
 	if (map_value_has_spin_lock(map)) {
 		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {
-- 
2.30.2

[PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
Then use call_rcu() to wait for normal progs to finish
and finally do free_one() on each element when freeing objects
into global memory pool.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/memalloc.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 9e5ad7dc4dc7..d34383dc12d9 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -224,6 +224,13 @@ static void __free_rcu(struct rcu_head *head)
 	atomic_set(&c->call_rcu_in_progress, 0);
 }
 
+static void __free_rcu_tasks_trace(struct rcu_head *head)
+{
+	struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
+
+	call_rcu(&c->rcu, __free_rcu);
+}
+
 static void enque_to_free(struct bpf_mem_cache *c, void *obj)
 {
 	struct llist_node *llnode = obj;
@@ -249,7 +256,11 @@ static void do_call_rcu(struct bpf_mem_cache *c)
 		 * from __free_rcu() and from drain_mem_cache().
 		 */
 		__llist_add(llnode, &c->waiting_for_gp);
-	call_rcu(&c->rcu, __free_rcu);
+	/* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
+	 * Then use call_rcu() to wait for normal progs to finish
+	 * and finally do free_one() on each element.
+	 */
+	call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
 }
 
 static void free_bulk(struct bpf_mem_cache *c)
@@ -452,6 +463,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 		/* c->waiting_for_gp list was drained, but __free_rcu might
 		 * still execute. Wait for it now before we free 'c'.
 		 */
+		rcu_barrier_tasks_trace();
 		rcu_barrier();
 		free_percpu(ma->cache);
 		ma->cache = NULL;
-- 
2.30.2

[PATCH v3 bpf-next 14/15] bpf: Remove prealloc-only restriction for sleepable bpf programs.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Since hash map is now converted to bpf_mem_alloc and it's waiting for rcu and
rcu_tasks_trace GPs before freeing elements into global memory slabs it's safe
to use dynamically allocated hash maps in sleepable bpf programs.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 23 -----------------------
 1 file changed, 23 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a1ada707c57c..dcbcf876b886 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12562,14 +12562,6 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
 	return err;
 }
 
-static int check_map_prealloc(struct bpf_map *map)
-{
-	return (map->map_type != BPF_MAP_TYPE_HASH &&
-		map->map_type != BPF_MAP_TYPE_PERCPU_HASH &&
-		map->map_type != BPF_MAP_TYPE_HASH_OF_MAPS) ||
-		!(map->map_flags & BPF_F_NO_PREALLOC);
-}
-
 static bool is_tracing_prog_type(enum bpf_prog_type type)
 {
 	switch (type) {
@@ -12584,15 +12576,6 @@ static bool is_tracing_prog_type(enum bpf_prog_type type)
 	}
 }
 
-static bool is_preallocated_map(struct bpf_map *map)
-{
-	if (!check_map_prealloc(map))
-		return false;
-	if (map->inner_map_meta && !check_map_prealloc(map->inner_map_meta))
-		return false;
-	return true;
-}
-
 static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 					struct bpf_map *map,
 					struct bpf_prog *prog)
@@ -12645,12 +12628,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
 		case BPF_MAP_TYPE_ARRAY_OF_MAPS:
 		case BPF_MAP_TYPE_HASH_OF_MAPS:
-			if (!is_preallocated_map(map)) {
-				verbose(env,
-					"Sleepable programs can only use preallocated maps\n");
-				return -EINVAL;
-			}
-			break;
 		case BPF_MAP_TYPE_RINGBUF:
 		case BPF_MAP_TYPE_INODE_STORAGE:
 		case BPF_MAP_TYPE_SK_STORAGE:
-- 
2.30.2

[PATCH v3 bpf-next 15/15] bpf: Introduce sysctl kernel.bpf_force_dyn_alloc.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Introduce sysctl kernel.bpf_force_dyn_alloc to force dynamic allocation in bpf
hash map. All selftests/bpf should pass with bpf_force_dyn_alloc 0 or 1 and all
bpf programs (both sleepable and not) should not see any functional difference.
The sysctl's observable behavior should only be improved memory usage.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/filter.h | 2 ++
 kernel/bpf/core.c      | 2 ++
 kernel/bpf/hashtab.c   | 5 +++++
 kernel/bpf/syscall.c   | 9 +++++++++
 4 files changed, 18 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index a5f21dc3c432..eb4d4a0c0bde 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1009,6 +1009,8 @@ bpf_run_sk_reuseport(struct sock_reuseport *reuse, struct sock *sk,
 }
 #endif
 
+extern int bpf_force_dyn_alloc;
+
 #ifdef CONFIG_BPF_JIT
 extern int bpf_jit_enable;
 extern int bpf_jit_harden;
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 639437f36928..a13e78ea4b90 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -533,6 +533,8 @@ void bpf_prog_kallsyms_del_all(struct bpf_prog *fp)
 	bpf_prog_kallsyms_del(fp);
 }
 
+int bpf_force_dyn_alloc __read_mostly;
+
 #ifdef CONFIG_BPF_JIT
 /* All BPF JIT sysctl knobs here. */
 int bpf_jit_enable   __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 89f26cbddef5..f68a3400939e 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -505,6 +505,11 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 
 	bpf_map_init_from_attr(&htab->map, attr);
 
+	if (!lru && bpf_force_dyn_alloc) {
+		prealloc = false;
+		htab->map.map_flags |= BPF_F_NO_PREALLOC;
+	}
+
 	if (percpu_lru) {
 		/* ensure each CPU's lru list has >=1 elements.
 		 * since we are at it, make each lru list has the same
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 850270a72350..c201796f4997 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5297,6 +5297,15 @@ static struct ctl_table bpf_syscall_table[] = {
 		.mode		= 0644,
 		.proc_handler	= bpf_stats_handler,
 	},
+	{
+		.procname	= "bpf_force_dyn_alloc",
+		.data		= &bpf_force_dyn_alloc,
+		.maxlen		= sizeof(int),
+		.mode		= 0600,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 	{ }
 };
 
-- 
2.30.2

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Kumar Kartikeya Dwivedi]

On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> Then use call_rcu() to wait for normal progs to finish
> and finally do free_one() on each element when freeing objects
> into global memory pool.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---

I fear this can make OOM issues very easy to run into, because one
sleepable prog that sleeps for a long period of time can hold the
freeing of elements from another sleepable prog which either does not
sleep often or sleeps for a very short period of time, and has a high
update frequency. I'm mostly worried that unrelated sleepable programs
not even using the same map will begin to affect each other.

Have you considered other options? E.g. we could directly expose
bpf_rcu_read_lock/bpf_rcu_read_unlock to the program and enforce that
access to RCU protected map lookups only happens in such read
sections, and unlock invalidates all RCU protected pointers? Sleepable
helpers can then not be invoked inside the BPF RCU read section. The
program uses RCU read section while accessing such maps, and sleeps
after doing bpf_rcu_read_unlock. They can be kfuncs.

It might also be useful in general, to access RCU protected data from
sleepable programs (i.e. make some sections of the program RCU
protected and non-sleepable at runtime). It will allow use of elements
from dynamically allocated maps with bpf_mem_alloc while not having to
wait for RCU tasks trace grace period, which can extend into minutes
(or even longer if unlucky).

One difference would be that you can pin a lookup across a sleep cycle
with this approach, but not with preallocated maps or the explicit RCU
section above, but I'm not sure it's worth it. It isn't possible now.

>  kernel/bpf/memalloc.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> index 9e5ad7dc4dc7..d34383dc12d9 100644
> --- a/kernel/bpf/memalloc.c
> +++ b/kernel/bpf/memalloc.c
> @@ -224,6 +224,13 @@ static void __free_rcu(struct rcu_head *head)
>         atomic_set(&c->call_rcu_in_progress, 0);
>  }
>
> +static void __free_rcu_tasks_trace(struct rcu_head *head)
> +{
> +       struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
> +
> +       call_rcu(&c->rcu, __free_rcu);
> +}
> +
>  static void enque_to_free(struct bpf_mem_cache *c, void *obj)
>  {
>         struct llist_node *llnode = obj;
> @@ -249,7 +256,11 @@ static void do_call_rcu(struct bpf_mem_cache *c)
>                  * from __free_rcu() and from drain_mem_cache().
>                  */
>                 __llist_add(llnode, &c->waiting_for_gp);
> -       call_rcu(&c->rcu, __free_rcu);
> +       /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> +        * Then use call_rcu() to wait for normal progs to finish
> +        * and finally do free_one() on each element.
> +        */
> +       call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
>  }
>
>  static void free_bulk(struct bpf_mem_cache *c)
> @@ -452,6 +463,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
>                 /* c->waiting_for_gp list was drained, but __free_rcu might
>                  * still execute. Wait for it now before we free 'c'.
>                  */
> +               rcu_barrier_tasks_trace();
>                 rcu_barrier();
>                 free_percpu(ma->cache);
>                 ma->cache = NULL;
> --
> 2.30.2
>

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Alexei Starovoitov]

On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > From: Alexei Starovoitov <ast@kernel.org>
> >
> > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > Then use call_rcu() to wait for normal progs to finish
> > and finally do free_one() on each element when freeing objects
> > into global memory pool.
> >
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > ---
> 
> I fear this can make OOM issues very easy to run into, because one
> sleepable prog that sleeps for a long period of time can hold the
> freeing of elements from another sleepable prog which either does not
> sleep often or sleeps for a very short period of time, and has a high
> update frequency. I'm mostly worried that unrelated sleepable programs
> not even using the same map will begin to affect each other.

'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
sleepable progs can copy_from_user, but they're not allowed to waste time.
I don't share OOM concerns at all.
max_entries and memcg limits are still there and enforced.
dynamic map is strictly better and memory efficient than full prealloc.

> Have you considered other options? E.g. we could directly expose
> bpf_rcu_read_lock/bpf_rcu_read_unlock to the program and enforce that
> access to RCU protected map lookups only happens in such read
> sections, and unlock invalidates all RCU protected pointers? Sleepable
> helpers can then not be invoked inside the BPF RCU read section. The
> program uses RCU read section while accessing such maps, and sleeps
> after doing bpf_rcu_read_unlock. They can be kfuncs.

Yes. We can add explicit bpf_rcu_read_lock and teach verifier about RCU CS,
but I don't see the value specifically for sleepable progs.
Current sleepable progs can do map lookup without extra kfuncs.
Explicit CS would force progs to be rewritten which is not great.

> It might also be useful in general, to access RCU protected data from
> sleepable programs (i.e. make some sections of the program RCU
> protected and non-sleepable at runtime). It will allow use of elements

For other cases, sure. We can introduce RCU protected objects and
explicit bpf_rcu_read_lock.

> from dynamically allocated maps with bpf_mem_alloc while not having to
> wait for RCU tasks trace grace period, which can extend into minutes
> (or even longer if unlucky).

sleepable bpf prog that lasts minutes? In what kind of situation?
We don't have bpf_sleep() helper and not going to add one any time soon.

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Kumar Kartikeya Dwivedi]

On Sat, 20 Aug 2022 at 00:43, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > From: Alexei Starovoitov <ast@kernel.org>
> > >
> > > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > > Then use call_rcu() to wait for normal progs to finish
> > > and finally do free_one() on each element when freeing objects
> > > into global memory pool.
> > >
> > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > ---
> >
> > I fear this can make OOM issues very easy to run into, because one
> > sleepable prog that sleeps for a long period of time can hold the
> > freeing of elements from another sleepable prog which either does not
> > sleep often or sleeps for a very short period of time, and has a high
> > update frequency. I'm mostly worried that unrelated sleepable programs
> > not even using the same map will begin to affect each other.
>
> 'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
> sleepable progs can copy_from_user, but they're not allowed to waste time.

It is certainly possible to waste time, but indirectly, not through
the BPF program itself.

If you have userfaultfd enabled (for unpriv users), an unprivileged
user can trap a sleepable BPF prog (say LSM) using bpf_copy_from_user
for as long as it wants. A similar case can be done using FUSE, IIRC.

You can then say it's a problem about unprivileged users being able to
use userfaultfd or FUSE, or we could think about fixing
bpf_copy_from_user to return -EFAULT for this case, but it is totally
possible right now for malicious userspace to extend the tasks trace
gp like this for minutes (or even longer) on a system where sleepable
BPF programs are using e.g. bpf_copy_from_user.

> I don't share OOM concerns at all.
> max_entries and memcg limits are still there and enforced.
> dynamic map is strictly better and memory efficient than full prealloc.
>
> > Have you considered other options? E.g. we could directly expose
> > bpf_rcu_read_lock/bpf_rcu_read_unlock to the program and enforce that
> > access to RCU protected map lookups only happens in such read
> > sections, and unlock invalidates all RCU protected pointers? Sleepable
> > helpers can then not be invoked inside the BPF RCU read section. The
> > program uses RCU read section while accessing such maps, and sleeps
> > after doing bpf_rcu_read_unlock. They can be kfuncs.
>
> Yes. We can add explicit bpf_rcu_read_lock and teach verifier about RCU CS,
> but I don't see the value specifically for sleepable progs.
> Current sleepable progs can do map lookup without extra kfuncs.
> Explicit CS would force progs to be rewritten which is not great.
>
> > It might also be useful in general, to access RCU protected data from
> > sleepable programs (i.e. make some sections of the program RCU
> > protected and non-sleepable at runtime). It will allow use of elements
>
> For other cases, sure. We can introduce RCU protected objects and
> explicit bpf_rcu_read_lock.
>
> > from dynamically allocated maps with bpf_mem_alloc while not having to
> > wait for RCU tasks trace grace period, which can extend into minutes
> > (or even longer if unlucky).
>
> sleepable bpf prog that lasts minutes? In what kind of situation?
> We don't have bpf_sleep() helper and not going to add one any time soon.

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Alexei Starovoitov]

On Fri, Aug 19, 2022 at 3:56 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Sat, 20 Aug 2022 at 00:43, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > From: Alexei Starovoitov <ast@kernel.org>
> > > >
> > > > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > > > Then use call_rcu() to wait for normal progs to finish
> > > > and finally do free_one() on each element when freeing objects
> > > > into global memory pool.
> > > >
> > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > > ---
> > >
> > > I fear this can make OOM issues very easy to run into, because one
> > > sleepable prog that sleeps for a long period of time can hold the
> > > freeing of elements from another sleepable prog which either does not
> > > sleep often or sleeps for a very short period of time, and has a high
> > > update frequency. I'm mostly worried that unrelated sleepable programs
> > > not even using the same map will begin to affect each other.
> >
> > 'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
> > sleepable progs can copy_from_user, but they're not allowed to waste time.
>
> It is certainly possible to waste time, but indirectly, not through
> the BPF program itself.
>
> If you have userfaultfd enabled (for unpriv users), an unprivileged
> user can trap a sleepable BPF prog (say LSM) using bpf_copy_from_user
> for as long as it wants. A similar case can be done using FUSE, IIRC.
>
> You can then say it's a problem about unprivileged users being able to
> use userfaultfd or FUSE, or we could think about fixing
> bpf_copy_from_user to return -EFAULT for this case, but it is totally
> possible right now for malicious userspace to extend the tasks trace
> gp like this for minutes (or even longer) on a system where sleepable
> BPF programs are using e.g. bpf_copy_from_user.

Well in that sense userfaultfd can keep all sorts of things
in the kernel from making progress.
But nothing to do with OOM.
There is still the max_entries limit.
The amount of objects in waiting_for_gp is guaranteed to be less
than full prealloc.

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Kumar Kartikeya Dwivedi]

On Sat, 20 Aug 2022 at 01:01, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Fri, Aug 19, 2022 at 3:56 PM Kumar Kartikeya Dwivedi
> <memxor@gmail.com> wrote:
> >
> > On Sat, 20 Aug 2022 at 00:43, Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> > > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > > <alexei.starovoitov@gmail.com> wrote:
> > > > >
> > > > > From: Alexei Starovoitov <ast@kernel.org>
> > > > >
> > > > > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > > > > Then use call_rcu() to wait for normal progs to finish
> > > > > and finally do free_one() on each element when freeing objects
> > > > > into global memory pool.
> > > > >
> > > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > > > ---
> > > >
> > > > I fear this can make OOM issues very easy to run into, because one
> > > > sleepable prog that sleeps for a long period of time can hold the
> > > > freeing of elements from another sleepable prog which either does not
> > > > sleep often or sleeps for a very short period of time, and has a high
> > > > update frequency. I'm mostly worried that unrelated sleepable programs
> > > > not even using the same map will begin to affect each other.
> > >
> > > 'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
> > > sleepable progs can copy_from_user, but they're not allowed to waste time.
> >
> > It is certainly possible to waste time, but indirectly, not through
> > the BPF program itself.
> >
> > If you have userfaultfd enabled (for unpriv users), an unprivileged
> > user can trap a sleepable BPF prog (say LSM) using bpf_copy_from_user
> > for as long as it wants. A similar case can be done using FUSE, IIRC.
> >
> > You can then say it's a problem about unprivileged users being able to
> > use userfaultfd or FUSE, or we could think about fixing
> > bpf_copy_from_user to return -EFAULT for this case, but it is totally
> > possible right now for malicious userspace to extend the tasks trace
> > gp like this for minutes (or even longer) on a system where sleepable
> > BPF programs are using e.g. bpf_copy_from_user.
>
> Well in that sense userfaultfd can keep all sorts of things
> in the kernel from making progress.
> But nothing to do with OOM.
> There is still the max_entries limit.
> The amount of objects in waiting_for_gp is guaranteed to be less
> than full prealloc.

My thinking was that once you hold the GP using uffd, we can assume
you will eventually hit a case where all such maps on the system have
their max_entries exhausted. So yes, it probably won't OOM, but it
would be bad regardless.

I think this just begs instead that uffd (and even FUSE) should not be
available to untrusted processes on the system by default. Both are
used regularly to widen hard to hit race conditions in the kernel.

But anyway, there's no easy way currently to guarantee the lifetime of
elements for the sleepable case while being as low overhead as trace
RCU, so it makes sense to go ahead with this.

Re: [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

[Kumar Kartikeya Dwivedi]

On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
> kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
> and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
> solves the memory consumption issue, avoids kmem_cache_destroy latency and
> keeps bpf hash map performance the same.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Makes sense, there was a call_rcu_lazy work from Joel (CCed) on doing
this batching using a timer + max batch count instead, I wonder if
that fits our use case and could be useful in the future when it is
merged?

https://lore.kernel.org/rcu/20220713213237.1596225-2-joel@joelfernandes.org

wdyt?

> ---
>  kernel/bpf/memalloc.c | 64 +++++++++++++++++++++++++++++++++++++++++--
>  kernel/bpf/syscall.c  |  5 +++-
>  2 files changed, 65 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> index 22b729914afe..d765a5cb24b4 100644
> --- a/kernel/bpf/memalloc.c
> +++ b/kernel/bpf/memalloc.c
> @@ -100,6 +100,11 @@ struct bpf_mem_cache {
>         /* count of objects in free_llist */
>         int free_cnt;
>         int low_watermark, high_watermark, batch;
> +
> +       struct rcu_head rcu;
> +       struct llist_head free_by_rcu;
> +       struct llist_head waiting_for_gp;
> +       atomic_t call_rcu_in_progress;
>  };
>
>  struct bpf_mem_caches {
> @@ -188,6 +193,45 @@ static void free_one(struct bpf_mem_cache *c, void *obj)
>                 kfree(obj);
>  }
>
> +static void __free_rcu(struct rcu_head *head)
> +{
> +       struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
> +       struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
> +       struct llist_node *pos, *t;
> +
> +       llist_for_each_safe(pos, t, llnode)
> +               free_one(c, pos);
> +       atomic_set(&c->call_rcu_in_progress, 0);
> +}
> +
> +static void enque_to_free(struct bpf_mem_cache *c, void *obj)
> +{
> +       struct llist_node *llnode = obj;
> +
> +       /* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
> +        * Nothing races to add to free_by_rcu list.
> +        */
> +       __llist_add(llnode, &c->free_by_rcu);
> +}
> +
> +static void do_call_rcu(struct bpf_mem_cache *c)
> +{
> +       struct llist_node *llnode, *t;
> +
> +       if (atomic_xchg(&c->call_rcu_in_progress, 1))
> +               return;
> +
> +       WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
> +       llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
> +               /* There is no concurrent __llist_add(waiting_for_gp) access.
> +                * It doesn't race with llist_del_all either.
> +                * But there could be two concurrent llist_del_all(waiting_for_gp):
> +                * from __free_rcu() and from drain_mem_cache().
> +                */
> +               __llist_add(llnode, &c->waiting_for_gp);
> +       call_rcu(&c->rcu, __free_rcu);
> +}
> +
>  static void free_bulk(struct bpf_mem_cache *c)
>  {
>         struct llist_node *llnode, *t;
> @@ -207,12 +251,13 @@ static void free_bulk(struct bpf_mem_cache *c)
>                 local_dec(&c->active);
>                 if (IS_ENABLED(CONFIG_PREEMPT_RT))
>                         local_irq_restore(flags);
> -               free_one(c, llnode);
> +               enque_to_free(c, llnode);
>         } while (cnt > (c->high_watermark + c->low_watermark) / 2);
>
>         /* and drain free_llist_extra */
>         llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
> -               free_one(c, llnode);
> +               enque_to_free(c, llnode);
> +       do_call_rcu(c);
>  }
>
>  static void bpf_mem_refill(struct irq_work *work)
> @@ -298,7 +343,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
>                         return -ENOMEM;
>                 size += LLIST_NODE_SZ; /* room for llist_node */
>                 snprintf(buf, sizeof(buf), "bpf-%u", size);
> -               kmem_cache = kmem_cache_create(buf, size, 8, SLAB_TYPESAFE_BY_RCU, NULL);
> +               kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
>                 if (!kmem_cache) {
>                         free_percpu(pc);
>                         return -ENOMEM;
> @@ -340,6 +385,15 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
>  {
>         struct llist_node *llnode, *t;
>
> +       /* The caller has done rcu_barrier() and no progs are using this
> +        * bpf_mem_cache, but htab_map_free() called bpf_mem_cache_free() for
> +        * all remaining elements and they can be in free_by_rcu or in
> +        * waiting_for_gp lists, so drain those lists now.
> +        */
> +       llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
> +               free_one(c, llnode);
> +       llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
> +               free_one(c, llnode);
>         llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
>                 free_one(c, llnode);
>         llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
> @@ -361,6 +415,10 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
>                 kmem_cache_destroy(c->kmem_cache);
>                 if (c->objcg)
>                         obj_cgroup_put(c->objcg);
> +               /* c->waiting_for_gp list was drained, but __free_rcu might
> +                * still execute. Wait for it now before we free 'c'.
> +                */
> +               rcu_barrier();
>                 free_percpu(ma->cache);
>                 ma->cache = NULL;
>         }
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a4d40d98428a..850270a72350 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -638,7 +638,10 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
>                 bpf_map_free_id(map, do_idr_lock);
>                 btf_put(map->btf);
>                 INIT_WORK(&map->work, bpf_map_free_deferred);
> -               schedule_work(&map->work);
> +               /* Avoid spawning kworkers, since they all might contend
> +                * for the same mutex like slab_mutex.
> +                */
> +               queue_work(system_unbound_wq, &map->work);
>         }
>  }
>
> --
> 2.30.2
>

Re: [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator.

[Kumar Kartikeya Dwivedi]

On Fri, 19 Aug 2022 at 23:42, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> Introduce any context BPF specific memory allocator.
>
> Tracing BPF programs can attach to kprobe and fentry. Hence they
> run in unknown context where calling plain kmalloc() might not be safe.
> Front-end kmalloc() with per-cpu cache of free elements.
> Refill this cache asynchronously from irq_work.
>
> Major achievements enabled by bpf_mem_alloc:
> - Dynamically allocated hash maps used to be 10 times slower than fully preallocated.
>   With bpf_mem_alloc and subsequent optimizations the speed of dynamic maps is equal to full prealloc.
> - Tracing bpf programs can use dynamically allocated hash maps.
>   Potentially saving lots of memory. Typical hash map is sparsely populated.
> - Sleepable bpf programs can used dynamically allocated hash maps.
>

From my side, for the whole series:
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>


> v2->v3:
> - Rewrote the free_list algorithm based on discussions with Kumar. Patch 1.
> - Allowed sleepable bpf progs use dynamically allocated maps. Patches 13 and 14.
> - Added sysctl to force bpf_mem_alloc in hash map even if pre-alloc is
>   requested to reduce memory consumption. Patch 15.
> - Fix: zero-fill percpu allocation
> - Single rcu_barrier at the end instead of each cpu during bpf_mem_alloc destruction
>
> v2 thread:
> https://lore.kernel.org/bpf/20220817210419.95560-1-alexei.starovoitov@gmail.com/
>
> v1->v2:
> - Moved unsafe direct call_rcu() from hash map into safe place inside bpf_mem_alloc. Patches 7 and 9.
> - Optimized atomic_inc/dec in hash map with percpu_counter. Patch 6.
> - Tuned watermarks per allocation size. Patch 8
> - Adopted this approach to per-cpu allocation. Patch 10.
> - Fully converted hash map to bpf_mem_alloc. Patch 11.
> - Removed tracing prog restriction on map types. Combination of all patches and final patch 12.
>
> v1 thread:
> https://lore.kernel.org/bpf/20220623003230.37497-1-alexei.starovoitov@gmail.com/
>
> LWN article:
> https://lwn.net/Articles/899274/
>
> Future work:
> - expose bpf_mem_alloc as uapi FD to be used in dynptr_alloc, kptr_alloc
> - convert lru map to bpf_mem_alloc
>
> Alexei Starovoitov (15):
>   bpf: Introduce any context BPF specific memory allocator.
>   bpf: Convert hash map to bpf_mem_alloc.
>   selftests/bpf: Improve test coverage of test_maps
>   samples/bpf: Reduce syscall overhead in map_perf_test.
>   bpf: Relax the requirement to use preallocated hash maps in tracing
>     progs.
>   bpf: Optimize element count in non-preallocated hash map.
>   bpf: Optimize call_rcu in non-preallocated hash map.
>   bpf: Adjust low/high watermarks in bpf_mem_cache
>   bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.
>   bpf: Add percpu allocation support to bpf_mem_alloc.
>   bpf: Convert percpu hash map to per-cpu bpf_mem_alloc.
>   bpf: Remove tracing program restriction on map types
>   bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.
>   bpf: Remove prealloc-only restriction for sleepable bpf programs.
>   bpf: Introduce sysctl kernel.bpf_force_dyn_alloc.
>
>  include/linux/bpf_mem_alloc.h             |  26 +
>  include/linux/filter.h                    |   2 +
>  kernel/bpf/Makefile                       |   2 +-
>  kernel/bpf/core.c                         |   2 +
>  kernel/bpf/hashtab.c                      | 132 +++--
>  kernel/bpf/memalloc.c                     | 601 ++++++++++++++++++++++
>  kernel/bpf/syscall.c                      |  14 +-
>  kernel/bpf/verifier.c                     |  52 --
>  samples/bpf/map_perf_test_kern.c          |  44 +-
>  samples/bpf/map_perf_test_user.c          |   2 +-
>  tools/testing/selftests/bpf/progs/timer.c |  11 -
>  tools/testing/selftests/bpf/test_maps.c   |  38 +-
>  12 files changed, 795 insertions(+), 131 deletions(-)
>  create mode 100644 include/linux/bpf_mem_alloc.h
>  create mode 100644 kernel/bpf/memalloc.c
>
> --
> 2.30.2
>

Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

[Alexei Starovoitov]

On Wed, Aug 24, 2022 at 12:50 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Sat, 20 Aug 2022 at 01:01, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Fri, Aug 19, 2022 at 3:56 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.com> wrote:
> > >
> > > On Sat, 20 Aug 2022 at 00:43, Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> > > > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > > > <alexei.starovoitov@gmail.com> wrote:
> > > > > >
> > > > > > From: Alexei Starovoitov <ast@kernel.org>
> > > > > >
> > > > > > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > > > > > Then use call_rcu() to wait for normal progs to finish
> > > > > > and finally do free_one() on each element when freeing objects
> > > > > > into global memory pool.
> > > > > >
> > > > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > > > > ---
> > > > >
> > > > > I fear this can make OOM issues very easy to run into, because one
> > > > > sleepable prog that sleeps for a long period of time can hold the
> > > > > freeing of elements from another sleepable prog which either does not
> > > > > sleep often or sleeps for a very short period of time, and has a high
> > > > > update frequency. I'm mostly worried that unrelated sleepable programs
> > > > > not even using the same map will begin to affect each other.
> > > >
> > > > 'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
> > > > sleepable progs can copy_from_user, but they're not allowed to waste time.
> > >
> > > It is certainly possible to waste time, but indirectly, not through
> > > the BPF program itself.
> > >
> > > If you have userfaultfd enabled (for unpriv users), an unprivileged
> > > user can trap a sleepable BPF prog (say LSM) using bpf_copy_from_user
> > > for as long as it wants. A similar case can be done using FUSE, IIRC.
> > >
> > > You can then say it's a problem about unprivileged users being able to
> > > use userfaultfd or FUSE, or we could think about fixing
> > > bpf_copy_from_user to return -EFAULT for this case, but it is totally
> > > possible right now for malicious userspace to extend the tasks trace
> > > gp like this for minutes (or even longer) on a system where sleepable
> > > BPF programs are using e.g. bpf_copy_from_user.
> >
> > Well in that sense userfaultfd can keep all sorts of things
> > in the kernel from making progress.
> > But nothing to do with OOM.
> > There is still the max_entries limit.
> > The amount of objects in waiting_for_gp is guaranteed to be less
> > than full prealloc.
>
> My thinking was that once you hold the GP using uffd, we can assume
> you will eventually hit a case where all such maps on the system have
> their max_entries exhausted. So yes, it probably won't OOM, but it
> would be bad regardless.
>
> I think this just begs instead that uffd (and even FUSE) should not be
> available to untrusted processes on the system by default. Both are
> used regularly to widen hard to hit race conditions in the kernel.
>
> But anyway, there's no easy way currently to guarantee the lifetime of
> elements for the sleepable case while being as low overhead as trace
> RCU, so it makes sense to go ahead with this.

Right. We evaluated SRCU for sleepable and it had too much overhead.
That's the reason rcu_tasks_trace was added and sleepable bpf progs
is the only user so far.
The point I'm arguing is that call_rcu_tasks_trace in this patch
doesn't add mm concerns more than the existing call_rcu.
There is CONFIG_PREEMPT_RCU and RT. uffd will cause similar
issues in such configs too.

Re: [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

[Alexei Starovoitov]

On Wed, Aug 24, 2022 at 12:59 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > From: Alexei Starovoitov <ast@kernel.org>
> >
> > SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
> > kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
> > and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
> > solves the memory consumption issue, avoids kmem_cache_destroy latency and
> > keeps bpf hash map performance the same.
> >
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
>
> Makes sense, there was a call_rcu_lazy work from Joel (CCed) on doing
> this batching using a timer + max batch count instead, I wonder if
> that fits our use case and could be useful in the future when it is
> merged?
>
> https://lore.kernel.org/rcu/20220713213237.1596225-2-joel@joelfernandes.org

Thanks for the pointer. It looks orthogonal.
timer based call_rcu is for power savings.
I'm not sure how it would help here. Probably wouldn't hurt.
But explicit waiting_for_gp list is necessary here,
because two later patches (sleepable support and per-cpu rcu-safe
freeing) are relying on this patch.

Re: [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator.

[Alexei Starovoitov]

On Wed, Aug 24, 2022 at 1:03 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Fri, 19 Aug 2022 at 23:42, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > From: Alexei Starovoitov <ast@kernel.org>
> >
> > Introduce any context BPF specific memory allocator.
> >
> > Tracing BPF programs can attach to kprobe and fentry. Hence they
> > run in unknown context where calling plain kmalloc() might not be safe.
> > Front-end kmalloc() with per-cpu cache of free elements.
> > Refill this cache asynchronously from irq_work.
> >
> > Major achievements enabled by bpf_mem_alloc:
> > - Dynamically allocated hash maps used to be 10 times slower than fully preallocated.
> >   With bpf_mem_alloc and subsequent optimizations the speed of dynamic maps is equal to full prealloc.
> > - Tracing bpf programs can use dynamically allocated hash maps.
> >   Potentially saving lots of memory. Typical hash map is sparsely populated.
> > - Sleepable bpf programs can used dynamically allocated hash maps.
> >
>
> From my side, for the whole series:
> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Thanks a bunch for all the suggestions.
Especially for ideas that led to rewrite of patch 1.
It looks much simpler now.

I've missed #include <asm/local.h> in the patch 1.
In the respin I'm going to keep your Ack if you don't mind.

Thanks!

Re: [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

[Joel Fernandes]

On Wed, Aug 24, 2022 at 8:14 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Aug 24, 2022 at 12:59 PM Kumar Kartikeya Dwivedi
> <memxor@gmail.com> wrote:
> >
> > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > From: Alexei Starovoitov <ast@kernel.org>
> > >
> > > SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
> > > kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
> > > and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
> > > solves the memory consumption issue, avoids kmem_cache_destroy latency and
> > > keeps bpf hash map performance the same.
> > >
> > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> >
> > Makes sense, there was a call_rcu_lazy work from Joel (CCed) on doing
> > this batching using a timer + max batch count instead, I wonder if
> > that fits our use case and could be useful in the future when it is
> > merged?
> >
> > https://lore.kernel.org/rcu/20220713213237.1596225-2-joel@joelfernandes.org
>
> Thanks for the pointer. It looks orthogonal.
> timer based call_rcu is for power savings.
> I'm not sure how it would help here. Probably wouldn't hurt.
> But explicit waiting_for_gp list is necessary here,
> because two later patches (sleepable support and per-cpu rcu-safe
> freeing) are relying on this patch.

Hello Kumar and Alexei,

Kumar thanks for the CC. I am seeing this BPF work for the first time
so have not gone over it too much - but in case the waiting is
synchronous by any chance, call_rcu_lazy() could hurt. The idea is to
only queue callbacks that are not all that important to the system
while keeping it quiet (power being the primary reason but Daniel
Bristot would concur it brings down OS noise and helps RT as well).

Have a good evening, Thank you,

 - Joel

Re: [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.

[Joel Fernandes]

On Wed, Aug 24, 2022 at 8:35 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> On Wed, Aug 24, 2022 at 8:14 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Aug 24, 2022 at 12:59 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.com> wrote:
> > >
> > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > From: Alexei Starovoitov <ast@kernel.org>
> > > >
> > > > SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
> > > > kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
> > > > and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
> > > > solves the memory consumption issue, avoids kmem_cache_destroy latency and
> > > > keeps bpf hash map performance the same.
> > > >
> > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > >
> > > Makes sense, there was a call_rcu_lazy work from Joel (CCed) on doing
> > > this batching using a timer + max batch count instead, I wonder if
> > > that fits our use case and could be useful in the future when it is
> > > merged?
> > >
> > > https://lore.kernel.org/rcu/20220713213237.1596225-2-joel@joelfernandes.org
> >
> > Thanks for the pointer. It looks orthogonal.
> > timer based call_rcu is for power savings.
> > I'm not sure how it would help here. Probably wouldn't hurt.
> > But explicit waiting_for_gp list is necessary here,
> > because two later patches (sleepable support and per-cpu rcu-safe
> > freeing) are relying on this patch.
>
> Hello Kumar and Alexei,
>
> Kumar thanks for the CC. I am seeing this BPF work for the first time
> so have not gone over it too much - but in case the waiting is
> synchronous by any chance, call_rcu_lazy() could hurt. The idea is to
> only queue callbacks that are not all that important to the system
> while keeping it quiet (power being the primary reason but Daniel
> Bristot would concur it brings down OS noise and helps RT as well).

Just as FYI, I see rcu_barrier() used in Alexei's patch - that will
flush the lazy CBs to keep rcu_barrier() both correct and performant.
At that point call_rcu_lazy() is equivalent to call_rcu() as we  no
longer kept the callbacks a secret from the rest of the system.

Thanks,

 -  Joel