[PATCH bpf-next v8 0/6] bpf, mm: Introduce try_alloc_pages()

[PATCH bpf-next v8 0/6] bpf, mm: Introduce try_alloc_pages()

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Hi All,

The main motivation is to make alloc page and slab reentrant and
remove bpf_mem_alloc.

v7->v8:
- rebase: s/free_unref_page/free_frozen_page/

v6->v7:
- Took Sebastian's patch for localtry_lock_t as-is with minor
  addition of local_trylock_acquire() for proper LOCKDEP.
  Kept his authorship.
- Adjusted patch 4 to use it. The rest is unchanged.

v6:
https://lore.kernel.org/bpf/20250124035655.78899-1-alexei.starovoitov@gmail.com/

v5->v6:
- Addressed comments from Sebastian, Vlastimil
- New approach for local_lock_t in patch 3. Instead of unconditionally
  increasing local_lock_t size to 4 bytes introduce local_trylock_t
  and use _Generic() tricks to manipulate active field.
- Address stackdepot reentrance issues. alloc part in patch 1 and
  free part in patch 2.
- Inlined mem_cgroup_cancel_charge() in patch 4 since this helper
  is being removed.
- Added Acks.
- Dropped failslab, kfence, kmemleak patch.
- Improved bpf_map_alloc_pages() in patch 6 a bit to demo intended usage.
  It will be refactored further.
- Considered using __GFP_COMP in try_alloc_pages to simplify
  free_pages_nolock a bit, but then decided to make it work
  for all types of pages, since free_pages_nolock() is used by
  stackdepot and currently it's using non-compound order 2.
  I felt it's best to leave it as-is and make free_pages_nolock()
  support all pages.

v5:
https://lore.kernel.org/all/20250115021746.34691-1-alexei.starovoitov@gmail.com/

v4->v5:
- Fixed patch 1 and 4 commit logs and comments per Michal suggestions.
  Added Acks.
- Added patch 6 to make failslab, kfence, kmemleak complaint
  with trylock mode. It's a prerequisite for reentrant slab patches.

v4:
https://lore.kernel.org/bpf/20250114021922.92609-1-alexei.starovoitov@gmail.com/

v3->v4:
Addressed feedback from Michal and Shakeel:
- GFP_TRYLOCK flag is gone. gfpflags_allow_spinning() is used instead.
- Improved comments and commit logs.

v3:
https://lore.kernel.org/bpf/20241218030720.1602449-1-alexei.starovoitov@gmail.com/

v2->v3:
To address the issues spotted by Sebastian, Vlastimil, Steven:
- Made GFP_TRYLOCK internal to mm/internal.h
  try_alloc_pages() and free_pages_nolock() are the only interfaces.
- Since spin_trylock() is not safe in RT from hard IRQ and NMI
  disable such usage in lock_trylock and in try_alloc_pages().
  In such case free_pages_nolock() falls back to llist right away.
- Process trylock_free_pages llist when preemptible.
- Check for things like unaccepted memory and order <= 3 early.
- Don't call into __alloc_pages_slowpath() at all.
- Inspired by Vlastimil's struct local_tryirq_lock adopted it in
  local_lock_t. Extra 4 bytes in !RT in local_lock_t shouldn't
  affect any of the current local_lock_t users. This is patch 3.
- Tested with bpf selftests in RT and !RT and realized how much
  more work is necessary on bpf side to play nice with RT.
  The urgency of this work got higher. The alternative is to
  convert bpf bits left and right to bpf_mem_alloc.

v2:
https://lore.kernel.org/bpf/20241210023936.46871-1-alexei.starovoitov@gmail.com/

v1->v2:
- fixed buggy try_alloc_pages_noprof() in PREEMPT_RT. Thanks Peter.
- optimize all paths by doing spin_trylock_irqsave() first
  and only then check for gfp_flags & __GFP_TRYLOCK.
  Then spin_lock_irqsave() if it's a regular mode.
  So new gfp flag will not add performance overhead.
- patches 2-5 are new. They introduce lockless and/or trylock free_pages_nolock()
  and memcg support. So it's in usable shape for bpf in patch 6.

v1:
https://lore.kernel.org/bpf/20241116014854.55141-1-alexei.starovoitov@gmail.com/

Alexei Starovoitov (5):
  mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation
  mm, bpf: Introduce free_pages_nolock()
  memcg: Use trylock to access memcg stock_lock.
  mm, bpf: Use memcg in try_alloc_pages().
  bpf: Use try_alloc_pages() to allocate pages for bpf needs.

Sebastian Andrzej Siewior (1):
  locking/local_lock: Introduce localtry_lock_t

 include/linux/bpf.h                 |   2 +-
 include/linux/gfp.h                 |  23 ++++
 include/linux/local_lock.h          |  59 ++++++++
 include/linux/local_lock_internal.h | 123 +++++++++++++++++
 include/linux/mm_types.h            |   4 +
 include/linux/mmzone.h              |   3 +
 kernel/bpf/arena.c                  |   5 +-
 kernel/bpf/syscall.c                |  23 +++-
 lib/stackdepot.c                    |  10 +-
 mm/internal.h                       |   1 +
 mm/memcontrol.c                     |  52 +++++---
 mm/page_alloc.c                     | 200 ++++++++++++++++++++++++++--
 mm/page_owner.c                     |   8 +-
 13 files changed, 472 insertions(+), 41 deletions(-)

-- 
2.43.5

[PATCH bpf-next v8 1/6] mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Tracing BPF programs execute from tracepoints and kprobes where
running context is unknown, but they need to request additional
memory. The prior workarounds were using pre-allocated memory and
BPF specific freelists to satisfy such allocation requests.
Instead, introduce gfpflags_allow_spinning() condition that signals
to the allocator that running context is unknown.
Then rely on percpu free list of pages to allocate a page.
try_alloc_pages() -> get_page_from_freelist() -> rmqueue() ->
rmqueue_pcplist() will spin_trylock to grab the page from percpu
free list. If it fails (due to re-entrancy or list being empty)
then rmqueue_bulk()/rmqueue_buddy() will attempt to
spin_trylock zone->lock and grab the page from there.
spin_trylock() is not safe in PREEMPT_RT when in NMI or in hard IRQ.
Bailout early in such case.

The support for gfpflags_allow_spinning() mode for free_page and memcg
comes in the next patches.

This is a first step towards supporting BPF requirements in SLUB
and getting rid of bpf_mem_alloc.
That goal was discussed at LSFMM: https://lwn.net/Articles/974138/

Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/gfp.h |  22 ++++++++++
 lib/stackdepot.c    |   5 ++-
 mm/internal.h       |   1 +
 mm/page_alloc.c     | 104 ++++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 127 insertions(+), 5 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 6bb1a5a7a4ae..5d9ee78c74e4 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -39,6 +39,25 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
 	return !!(gfp_flags & __GFP_DIRECT_RECLAIM);
 }
 
+static inline bool gfpflags_allow_spinning(const gfp_t gfp_flags)
+{
+	/*
+	 * !__GFP_DIRECT_RECLAIM -> direct claim is not allowed.
+	 * !__GFP_KSWAPD_RECLAIM -> it's not safe to wake up kswapd.
+	 * All GFP_* flags including GFP_NOWAIT use one or both flags.
+	 * try_alloc_pages() is the only API that doesn't specify either flag.
+	 *
+	 * This is stronger than GFP_NOWAIT or GFP_ATOMIC because
+	 * those are guaranteed to never block on a sleeping lock.
+	 * Here we are enforcing that the allocation doesn't ever spin
+	 * on any locks (i.e. only trylocks). There is no high level
+	 * GFP_$FOO flag for this use in try_alloc_pages() as the
+	 * regular page allocator doesn't fully support this
+	 * allocation mode.
+	 */
+	return !(gfp_flags & __GFP_RECLAIM);
+}
+
 #ifdef CONFIG_HIGHMEM
 #define OPT_ZONE_HIGHMEM ZONE_HIGHMEM
 #else
@@ -335,6 +354,9 @@ static inline struct page *alloc_page_vma_noprof(gfp_t gfp,
 }
 #define alloc_page_vma(...)			alloc_hooks(alloc_page_vma_noprof(__VA_ARGS__))
 
+struct page *try_alloc_pages_noprof(int nid, unsigned int order);
+#define try_alloc_pages(...)			alloc_hooks(try_alloc_pages_noprof(__VA_ARGS__))
+
 extern unsigned long get_free_pages_noprof(gfp_t gfp_mask, unsigned int order);
 #define __get_free_pages(...)			alloc_hooks(get_free_pages_noprof(__VA_ARGS__))
 
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 245d5b416699..377194969e61 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -591,7 +591,8 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
 	depot_stack_handle_t handle = 0;
 	struct page *page = NULL;
 	void *prealloc = NULL;
-	bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC;
+	bool allow_spin = gfpflags_allow_spinning(alloc_flags);
+	bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin;
 	unsigned long flags;
 	u32 hash;
 
@@ -630,7 +631,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
 			prealloc = page_address(page);
 	}
 
-	if (in_nmi()) {
+	if (in_nmi() || !allow_spin) {
 		/* We can never allocate in NMI context. */
 		WARN_ON_ONCE(can_alloc);
 		/* Best effort; bail if we fail to take the lock. */
diff --git a/mm/internal.h b/mm/internal.h
index 109ef30fee11..10a8b4b3b86e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1187,6 +1187,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 #define ALLOC_NOFRAGMENT	  0x0
 #endif
 #define ALLOC_HIGHATOMIC	0x200 /* Allows access to MIGRATE_HIGHATOMIC */
+#define ALLOC_TRYLOCK		0x400 /* Only use spin_trylock in allocation path */
 #define ALLOC_KSWAPD		0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */
 
 /* Flags that allow allocations below the min watermark. */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 579789600a3c..0404c4c0dfc7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2307,7 +2307,11 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
 	unsigned long flags;
 	int i;
 
-	spin_lock_irqsave(&zone->lock, flags);
+	if (!spin_trylock_irqsave(&zone->lock, flags)) {
+		if (unlikely(alloc_flags & ALLOC_TRYLOCK))
+			return 0;
+		spin_lock_irqsave(&zone->lock, flags);
+	}
 	for (i = 0; i < count; ++i) {
 		struct page *page = __rmqueue(zone, order, migratetype,
 								alloc_flags);
@@ -2907,7 +2911,11 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 
 	do {
 		page = NULL;
-		spin_lock_irqsave(&zone->lock, flags);
+		if (!spin_trylock_irqsave(&zone->lock, flags)) {
+			if (unlikely(alloc_flags & ALLOC_TRYLOCK))
+				return NULL;
+			spin_lock_irqsave(&zone->lock, flags);
+		}
 		if (alloc_flags & ALLOC_HIGHATOMIC)
 			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
 		if (!page) {
@@ -4511,7 +4519,12 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
 
 	might_alloc(gfp_mask);
 
-	if (should_fail_alloc_page(gfp_mask, order))
+	/*
+	 * Don't invoke should_fail logic, since it may call
+	 * get_random_u32() and printk() which need to spin_lock.
+	 */
+	if (!(*alloc_flags & ALLOC_TRYLOCK) &&
+	    should_fail_alloc_page(gfp_mask, order))
 		return false;
 
 	*alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, *alloc_flags);
@@ -7071,3 +7084,88 @@ static bool __free_unaccepted(struct page *page)
 }
 
 #endif /* CONFIG_UNACCEPTED_MEMORY */
+
+/**
+ * try_alloc_pages_noprof - opportunistic reentrant allocation from any context
+ * @nid - node to allocate from
+ * @order - allocation order size
+ *
+ * Allocates pages of a given order from the given node. This is safe to
+ * call from any context (from atomic, NMI, and also reentrant
+ * allocator -> tracepoint -> try_alloc_pages_noprof).
+ * Allocation is best effort and to be expected to fail easily so nobody should
+ * rely on the success. Failures are not reported via warn_alloc().
+ * See always fail conditions below.
+ *
+ * Return: allocated page or NULL on failure.
+ */
+struct page *try_alloc_pages_noprof(int nid, unsigned int order)
+{
+	/*
+	 * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
+	 * Do not specify __GFP_KSWAPD_RECLAIM either, since wake up of kswapd
+	 * is not safe in arbitrary context.
+	 *
+	 * These two are the conditions for gfpflags_allow_spinning() being true.
+	 *
+	 * Specify __GFP_NOWARN since failing try_alloc_pages() is not a reason
+	 * to warn. Also warn would trigger printk() which is unsafe from
+	 * various contexts. We cannot use printk_deferred_enter() to mitigate,
+	 * since the running context is unknown.
+	 *
+	 * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below
+	 * is safe in any context. Also zeroing the page is mandatory for
+	 * BPF use cases.
+	 *
+	 * Though __GFP_NOMEMALLOC is not checked in the code path below,
+	 * specify it here to highlight that try_alloc_pages()
+	 * doesn't want to deplete reserves.
+	 */
+	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC;
+	unsigned int alloc_flags = ALLOC_TRYLOCK;
+	struct alloc_context ac = { };
+	struct page *page;
+
+	/*
+	 * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is
+	 * unsafe in NMI. If spin_trylock() is called from hard IRQ the current
+	 * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will
+	 * mark the task as the owner of another rt_spin_lock which will
+	 * confuse PI logic, so return immediately if called form hard IRQ or
+	 * NMI.
+	 *
+	 * Note, irqs_disabled() case is ok. This function can be called
+	 * from raw_spin_lock_irqsave region.
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
+		return NULL;
+	if (!pcp_allowed_order(order))
+		return NULL;
+
+#ifdef CONFIG_UNACCEPTED_MEMORY
+	/* Bailout, since try_to_accept_memory_one() needs to take a lock */
+	if (has_unaccepted_memory())
+		return NULL;
+#endif
+	/* Bailout, since _deferred_grow_zone() needs to take a lock */
+	if (deferred_pages_enabled())
+		return NULL;
+
+	if (nid == NUMA_NO_NODE)
+		nid = numa_node_id();
+
+	prepare_alloc_pages(alloc_gfp, order, nid, NULL, &ac,
+			    &alloc_gfp, &alloc_flags);
+
+	/*
+	 * Best effort allocation from percpu free list.
+	 * If it's empty attempt to spin_trylock zone->lock.
+	 */
+	page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);
+
+	/* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */
+
+	trace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);
+	kmsan_alloc_page(page, order, alloc_gfp);
+	return page;
+}
-- 
2.43.5

[PATCH bpf-next v8 2/6] mm, bpf: Introduce free_pages_nolock()

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Introduce free_pages_nolock() that can free pages without taking locks.
It relies on trylock and can be called from any context.
Since spin_trylock() cannot be used in PREEMPT_RT from hard IRQ or NMI
it uses lockless link list to stash the pages which will be freed
by subsequent free_pages() from good context.

Do not use llist unconditionally. BPF maps continuously
allocate/free, so we cannot unconditionally delay the freeing to
llist. When the memory becomes free make it available to the
kernel and BPF users right away if possible, and fallback to
llist as the last resort.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/gfp.h      |  1 +
 include/linux/mm_types.h |  4 ++
 include/linux/mmzone.h   |  3 ++
 lib/stackdepot.c         |  5 ++-
 mm/page_alloc.c          | 90 +++++++++++++++++++++++++++++++++++-----
 mm/page_owner.c          |  8 +++-
 6 files changed, 98 insertions(+), 13 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 5d9ee78c74e4..ceb226c2e25c 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -379,6 +379,7 @@ __meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mas
 	__get_free_pages((gfp_mask) | GFP_DMA, (order))
 
 extern void __free_pages(struct page *page, unsigned int order);
+extern void free_pages_nolock(struct page *page, unsigned int order);
 extern void free_pages(unsigned long addr, unsigned int order);
 
 #define __free_page(page) __free_pages((page), 0)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 6b27db7f9496..483aa90242cd 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -99,6 +99,10 @@ struct page {
 				/* Or, free page */
 				struct list_head buddy_list;
 				struct list_head pcp_list;
+				struct {
+					struct llist_node pcp_llist;
+					unsigned int order;
+				};
 			};
 			/* See page-flags.h for PAGE_MAPPING_FLAGS */
 			struct address_space *mapping;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9540b41894da..e16939553930 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -972,6 +972,9 @@ struct zone {
 	/* Primarily protects free_area */
 	spinlock_t		lock;
 
+	/* Pages to be freed when next trylock succeeds */
+	struct llist_head	trylock_free_pages;
+
 	/* Write-intensive fields used by compaction and vmstats. */
 	CACHELINE_PADDING(_pad2_);
 
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 377194969e61..73d7b50924ef 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -672,7 +672,10 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
 exit:
 	if (prealloc) {
 		/* Stack depot didn't use this memory, free it. */
-		free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
+		if (!allow_spin)
+			free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER);
+		else
+			free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
 	}
 	if (found)
 		handle = found->handle.handle;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0404c4c0dfc7..3fbcbeb7de8e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -88,6 +88,9 @@ typedef int __bitwise fpi_t;
  */
 #define FPI_TO_TAIL		((__force fpi_t)BIT(1))
 
+/* Free the page without taking locks. Rely on trylock only. */
+#define FPI_TRYLOCK		((__force fpi_t)BIT(2))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
@@ -1249,13 +1252,44 @@ static void split_large_buddy(struct zone *zone, struct page *page,
 	} while (1);
 }
 
+static void add_page_to_zone_llist(struct zone *zone, struct page *page,
+				   unsigned int order)
+{
+	/* Remember the order */
+	page->order = order;
+	/* Add the page to the free list */
+	llist_add(&page->pcp_llist, &zone->trylock_free_pages);
+}
+
 static void free_one_page(struct zone *zone, struct page *page,
 			  unsigned long pfn, unsigned int order,
 			  fpi_t fpi_flags)
 {
+	struct llist_head *llhead;
 	unsigned long flags;
 
-	spin_lock_irqsave(&zone->lock, flags);
+	if (!spin_trylock_irqsave(&zone->lock, flags)) {
+		if (unlikely(fpi_flags & FPI_TRYLOCK)) {
+			add_page_to_zone_llist(zone, page, order);
+			return;
+		}
+		spin_lock_irqsave(&zone->lock, flags);
+	}
+
+	/* The lock succeeded. Process deferred pages. */
+	llhead = &zone->trylock_free_pages;
+	if (unlikely(!llist_empty(llhead) && !(fpi_flags & FPI_TRYLOCK))) {
+		struct llist_node *llnode;
+		struct page *p, *tmp;
+
+		llnode = llist_del_all(llhead);
+		llist_for_each_entry_safe(p, tmp, llnode, pcp_llist) {
+			unsigned int p_order = p->order;
+
+			split_large_buddy(zone, p, page_to_pfn(p), p_order, fpi_flags);
+			__count_vm_events(PGFREE, 1 << p_order);
+		}
+	}
 	split_large_buddy(zone, page, pfn, order, fpi_flags);
 	spin_unlock_irqrestore(&zone->lock, flags);
 
@@ -2599,7 +2633,7 @@ static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone,
 
 static void free_frozen_page_commit(struct zone *zone,
 		struct per_cpu_pages *pcp, struct page *page, int migratetype,
-		unsigned int order)
+		unsigned int order, fpi_t fpi_flags)
 {
 	int high, batch;
 	int pindex;
@@ -2634,6 +2668,14 @@ static void free_frozen_page_commit(struct zone *zone,
 	}
 	if (pcp->free_count < (batch << CONFIG_PCP_BATCH_SCALE_MAX))
 		pcp->free_count += (1 << order);
+
+	if (unlikely(fpi_flags & FPI_TRYLOCK)) {
+		/*
+		 * Do not attempt to take a zone lock. Let pcp->count get
+		 * over high mark temporarily.
+		 */
+		return;
+	}
 	high = nr_pcp_high(pcp, zone, batch, free_high);
 	if (pcp->count >= high) {
 		free_pcppages_bulk(zone, nr_pcp_free(pcp, batch, high, free_high),
@@ -2648,7 +2690,8 @@ static void free_frozen_page_commit(struct zone *zone,
 /*
  * Free a pcp page
  */
-void free_frozen_pages(struct page *page, unsigned int order)
+static void __free_frozen_pages(struct page *page, unsigned int order,
+				fpi_t fpi_flags)
 {
 	unsigned long __maybe_unused UP_flags;
 	struct per_cpu_pages *pcp;
@@ -2657,7 +2700,7 @@ void free_frozen_pages(struct page *page, unsigned int order)
 	int migratetype;
 
 	if (!pcp_allowed_order(order)) {
-		__free_pages_ok(page, order, FPI_NONE);
+		__free_pages_ok(page, order, fpi_flags);
 		return;
 	}
 
@@ -2675,23 +2718,33 @@ void free_frozen_pages(struct page *page, unsigned int order)
 	migratetype = get_pfnblock_migratetype(page, pfn);
 	if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
 		if (unlikely(is_migrate_isolate(migratetype))) {
-			free_one_page(zone, page, pfn, order, FPI_NONE);
+			free_one_page(zone, page, pfn, order, fpi_flags);
 			return;
 		}
 		migratetype = MIGRATE_MOVABLE;
 	}
 
+	if (unlikely((fpi_flags & FPI_TRYLOCK) && IS_ENABLED(CONFIG_PREEMPT_RT)
+		     && (in_nmi() || in_hardirq()))) {
+		add_page_to_zone_llist(zone, page, order);
+		return;
+	}
 	pcp_trylock_prepare(UP_flags);
 	pcp = pcp_spin_trylock(zone->per_cpu_pageset);
 	if (pcp) {
-		free_frozen_page_commit(zone, pcp, page, migratetype, order);
+		free_frozen_page_commit(zone, pcp, page, migratetype, order, fpi_flags);
 		pcp_spin_unlock(pcp);
 	} else {
-		free_one_page(zone, page, pfn, order, FPI_NONE);
+		free_one_page(zone, page, pfn, order, fpi_flags);
 	}
 	pcp_trylock_finish(UP_flags);
 }
 
+void free_frozen_pages(struct page *page, unsigned int order)
+{
+	__free_frozen_pages(page, order, FPI_NONE);
+}
+
 /*
  * Free a batch of folios
  */
@@ -2780,7 +2833,7 @@ void free_unref_folios(struct folio_batch *folios)
 
 		trace_mm_page_free_batched(&folio->page);
 		free_frozen_page_commit(zone, pcp, &folio->page, migratetype,
-				order);
+					order, FPI_NONE);
 	}
 
 	if (pcp) {
@@ -4841,22 +4894,37 @@ EXPORT_SYMBOL(get_zeroed_page_noprof);
  * Context: May be called in interrupt context or while holding a normal
  * spinlock, but not in NMI context or while holding a raw spinlock.
  */
-void __free_pages(struct page *page, unsigned int order)
+static void ___free_pages(struct page *page, unsigned int order,
+			  fpi_t fpi_flags)
 {
 	/* get PageHead before we drop reference */
 	int head = PageHead(page);
 	struct alloc_tag *tag = pgalloc_tag_get(page);
 
 	if (put_page_testzero(page))
-		free_frozen_pages(page, order);
+		__free_frozen_pages(page, order, fpi_flags);
 	else if (!head) {
 		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
 		while (order-- > 0)
-			free_frozen_pages(page + (1 << order), order);
+			__free_frozen_pages(page + (1 << order), order,
+					    fpi_flags);
 	}
 }
+void __free_pages(struct page *page, unsigned int order)
+{
+	___free_pages(page, order, FPI_NONE);
+}
 EXPORT_SYMBOL(__free_pages);
 
+/*
+ * Can be called while holding raw_spin_lock or from IRQ and NMI for any
+ * page type (not only those that came from try_alloc_pages)
+ */
+void free_pages_nolock(struct page *page, unsigned int order)
+{
+	___free_pages(page, order, FPI_TRYLOCK);
+}
+
 void free_pages(unsigned long addr, unsigned int order)
 {
 	if (addr != 0) {
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 2d6360eaccbb..90e31d0e3ed7 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -294,7 +294,13 @@ void __reset_page_owner(struct page *page, unsigned short order)
 	page_owner = get_page_owner(page_ext);
 	alloc_handle = page_owner->handle;
 
-	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
+	/*
+	 * Do not specify GFP_NOWAIT to make gfpflags_allow_spinning() == false
+	 * to prevent issues in stack_depot_save().
+	 * This is similar to try_alloc_pages() gfp flags, but only used
+	 * to signal stack_depot to avoid spin_locks.
+	 */
+	handle = save_stack(__GFP_NOWARN);
 	__update_page_owner_free_handle(page_ext, handle, order, current->pid,
 					current->tgid, free_ts_nsec);
 	page_ext_put(page_ext);
-- 
2.43.5

[PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Alexei Starovoitov]

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
critical section, but it doesn't prevent NMI, so the fully reentrant
code cannot use local_lock_irqsave() for exclusive access.

Introduce localtry_lock_t and localtry_lock_irqsave() that
disables interrupts and sets acquired=1, so localtry_lock_irqsave()
from NMI attempting to acquire the same lock will return false.

In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
Map localtry_lock_irqsave() to preemptible spin_trylock().
When in hard IRQ or NMI return false right away, since
spin_trylock() is not safe due to PI issues.

Note there is no need to use local_inc for acquired variable,
since it's a percpu variable with strict nesting scopes.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/local_lock.h          |  59 +++++++++++++
 include/linux/local_lock_internal.h | 123 ++++++++++++++++++++++++++++
 2 files changed, 182 insertions(+)

diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 091dc0b6bdfb..05c254a5d7d3 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -51,6 +51,65 @@
 #define local_unlock_irqrestore(lock, flags)			\
 	__local_unlock_irqrestore(lock, flags)
 
+/**
+ * localtry_lock_init - Runtime initialize a lock instance
+ */
+#define localtry_lock_init(lock)		__localtry_lock_init(lock)
+
+/**
+ * localtry_lock - Acquire a per CPU local lock
+ * @lock:	The lock variable
+ */
+#define localtry_lock(lock)		__localtry_lock(lock)
+
+/**
+ * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts
+ * @lock:	The lock variable
+ */
+#define localtry_lock_irq(lock)		__localtry_lock_irq(lock)
+
+/**
+ * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable
+ *			 interrupts
+ * @lock:	The lock variable
+ * @flags:	Storage for interrupt flags
+ */
+#define localtry_lock_irqsave(lock, flags)				\
+	__localtry_lock_irqsave(lock, flags)
+
+/**
+ * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
+ *			      interrupts if acquired
+ * @lock:	The lock variable
+ * @flags:	Storage for interrupt flags
+ *
+ * The function can be used in any context such as NMI or HARDIRQ. Due to
+ * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT.
+ */
+#define localtry_trylock_irqsave(lock, flags)				\
+	__localtry_trylock_irqsave(lock, flags)
+
+/**
+ * local_unlock - Release a per CPU local lock
+ * @lock:	The lock variable
+ */
+#define localtry_unlock(lock)		__localtry_unlock(lock)
+
+/**
+ * local_unlock_irq - Release a per CPU local lock and enable interrupts
+ * @lock:	The lock variable
+ */
+#define localtry_unlock_irq(lock)		__localtry_unlock_irq(lock)
+
+/**
+ * localtry_unlock_irqrestore - Release a per CPU local lock and restore
+ *			      interrupt flags
+ * @lock:	The lock variable
+ * @flags:      Interrupt flags to restore
+ */
+#define localtry_unlock_irqrestore(lock, flags)			\
+	__localtry_unlock_irqrestore(lock, flags)
+
 DEFINE_GUARD(local_lock, local_lock_t __percpu*,
 	     local_lock(_T),
 	     local_unlock(_T))
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index 8dd71fbbb6d2..c1369b300777 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -15,6 +15,11 @@ typedef struct {
 #endif
 } local_lock_t;
 
+typedef struct {
+	local_lock_t	llock;
+	unsigned int	acquired;
+} localtry_lock_t;
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define LOCAL_LOCK_DEBUG_INIT(lockname)		\
 	.dep_map = {					\
@@ -31,6 +36,13 @@ static inline void local_lock_acquire(local_lock_t *l)
 	l->owner = current;
 }
 
+static inline void local_trylock_acquire(local_lock_t *l)
+{
+	lock_map_acquire_try(&l->dep_map);
+	DEBUG_LOCKS_WARN_ON(l->owner);
+	l->owner = current;
+}
+
 static inline void local_lock_release(local_lock_t *l)
 {
 	DEBUG_LOCKS_WARN_ON(l->owner != current);
@@ -45,11 +57,13 @@ static inline void local_lock_debug_init(local_lock_t *l)
 #else /* CONFIG_DEBUG_LOCK_ALLOC */
 # define LOCAL_LOCK_DEBUG_INIT(lockname)
 static inline void local_lock_acquire(local_lock_t *l) { }
+static inline void local_trylock_acquire(local_lock_t *l) { }
 static inline void local_lock_release(local_lock_t *l) { }
 static inline void local_lock_debug_init(local_lock_t *l) { }
 #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 
 #define INIT_LOCAL_LOCK(lockname)	{ LOCAL_LOCK_DEBUG_INIT(lockname) }
+#define INIT_LOCALTRY_LOCK(lockname)	{ .llock = { LOCAL_LOCK_DEBUG_INIT(lockname.llock) }}
 
 #define __local_lock_init(lock)					\
 do {								\
@@ -118,6 +132,86 @@ do {								\
 #define __local_unlock_nested_bh(lock)				\
 	local_lock_release(this_cpu_ptr(lock))
 
+/* localtry_lock_t variants */
+
+#define __localtry_lock_init(lock)				\
+do {								\
+	__local_lock_init(&(lock)->llock);			\
+	WRITE_ONCE(&(lock)->acquired, 0);			\
+} while (0)
+
+#define __localtry_lock(lock)					\
+	do {							\
+		localtry_lock_t *lt;				\
+		preempt_disable();				\
+		lt = this_cpu_ptr(lock);			\
+		local_lock_acquire(&lt->llock);			\
+		WRITE_ONCE(lt->acquired, 1);			\
+	} while (0)
+
+#define __localtry_lock_irq(lock)				\
+	do {							\
+		localtry_lock_t *lt;				\
+		local_irq_disable();				\
+		lt = this_cpu_ptr(lock);			\
+		local_lock_acquire(&lt->llock);			\
+		WRITE_ONCE(lt->acquired, 1);			\
+	} while (0)
+
+#define __localtry_lock_irqsave(lock, flags)			\
+	do {							\
+		localtry_lock_t *lt;				\
+		local_irq_save(flags);				\
+		lt = this_cpu_ptr(lock);			\
+		local_lock_acquire(&lt->llock);			\
+		WRITE_ONCE(lt->acquired, 1);			\
+	} while (0)
+
+#define __localtry_trylock_irqsave(lock, flags)			\
+	({							\
+		localtry_lock_t *lt;				\
+		bool _ret;					\
+								\
+		local_irq_save(flags);				\
+		lt = this_cpu_ptr(lock);			\
+		if (!READ_ONCE(lt->acquired)) {			\
+			WRITE_ONCE(lt->acquired, 1);		\
+			local_trylock_acquire(&lt->llock);	\
+			_ret = true;				\
+		} else {					\
+			_ret = false;				\
+			local_irq_restore(flags);		\
+		}						\
+		_ret;						\
+	})
+
+#define __localtry_unlock(lock)					\
+	do {							\
+		localtry_lock_t *lt;				\
+		lt = this_cpu_ptr(lock);			\
+		WRITE_ONCE(lt->acquired, 0);			\
+		local_lock_release(&lt->llock);			\
+		preempt_enable();				\
+	} while (0)
+
+#define __localtry_unlock_irq(lock)				\
+	do {							\
+		localtry_lock_t *lt;				\
+		lt = this_cpu_ptr(lock);			\
+		WRITE_ONCE(lt->acquired, 0);			\
+		local_lock_release(&lt->llock);			\
+		local_irq_enable();				\
+	} while (0)
+
+#define __localtry_unlock_irqrestore(lock, flags)		\
+	do {							\
+		localtry_lock_t *lt;				\
+		lt = this_cpu_ptr(lock);			\
+		WRITE_ONCE(lt->acquired, 0);			\
+		local_lock_release(&lt->llock);			\
+		local_irq_restore(flags);			\
+	} while (0)
+
 #else /* !CONFIG_PREEMPT_RT */
 
 /*
@@ -125,8 +219,10 @@ do {								\
  * critical section while staying preemptible.
  */
 typedef spinlock_t local_lock_t;
+typedef spinlock_t localtry_lock_t;
 
 #define INIT_LOCAL_LOCK(lockname) __LOCAL_SPIN_LOCK_UNLOCKED((lockname))
+#define INIT_LOCALTRY_LOCK(lockname) INIT_LOCAL_LOCK(lockname)
 
 #define __local_lock_init(l)					\
 	do {							\
@@ -169,4 +265,31 @@ do {								\
 	spin_unlock(this_cpu_ptr((lock)));			\
 } while (0)
 
+/* localtry_lock_t variants */
+
+#define __localtry_lock_init(lock)			__local_lock_init(lock)
+#define __localtry_lock(lock)				__local_lock(lock)
+#define __localtry_lock_irq(lock)			__local_lock(lock)
+#define __localtry_lock_irqsave(lock, flags)		__local_lock_irqsave(lock, flags)
+#define __localtry_unlock(lock)				__local_unlock(lock)
+#define __localtry_unlock_irq(lock)			__local_unlock(lock)
+#define __localtry_unlock_irqrestore(lock, flags)	__local_unlock_irqrestore(lock, flags)
+
+#define __localtry_trylock_irqsave(lock, flags)			\
+	({							\
+		int __locked;					\
+								\
+		typecheck(unsigned long, flags);		\
+		flags = 0;					\
+		if (in_nmi() | in_hardirq()) {			\
+			__locked = 0;				\
+		} else {					\
+			migrate_disable();			\
+			__locked = spin_trylock(this_cpu_ptr((lock)));	\
+			if (!__locked)				\
+				migrate_enable();		\
+		}						\
+		__locked;					\
+	})
+
 #endif /* CONFIG_PREEMPT_RT */
-- 
2.43.5

[PATCH bpf-next v8 4/6] memcg: Use trylock to access memcg stock_lock.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Teach memcg to operate under trylock conditions when spinning locks
cannot be used.

localtry_trylock might fail and this would lead to charge cache bypass
if the calling context doesn't allow spinning (gfpflags_allow_spinning).
In those cases charge the memcg counter directly and fail early if
that is not possible. This might cause a pre-mature charge failing
but it will allow an opportunistic charging that is safe from
try_alloc_pages path.

Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 mm/memcontrol.c | 52 ++++++++++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 46f8b372d212..7587511b92cc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1739,7 +1739,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
 }
 
 struct memcg_stock_pcp {
-	local_lock_t stock_lock;
+	localtry_lock_t stock_lock;
 	struct mem_cgroup *cached; /* this never be root cgroup */
 	unsigned int nr_pages;
 
@@ -1754,7 +1754,7 @@ struct memcg_stock_pcp {
 #define FLUSHING_CACHED_CHARGE	0
 };
 static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = {
-	.stock_lock = INIT_LOCAL_LOCK(stock_lock),
+	.stock_lock = INIT_LOCALTRY_LOCK(stock_lock),
 };
 static DEFINE_MUTEX(percpu_charge_mutex);
 
@@ -1773,7 +1773,8 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
  *
  * returns true if successful, false otherwise.
  */
-static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
+static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages,
+			  gfp_t gfp_mask)
 {
 	struct memcg_stock_pcp *stock;
 	unsigned int stock_pages;
@@ -1783,7 +1784,11 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (nr_pages > MEMCG_CHARGE_BATCH)
 		return ret;
 
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	if (!localtry_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
+		if (!gfpflags_allow_spinning(gfp_mask))
+			return ret;
+		localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	}
 
 	stock = this_cpu_ptr(&memcg_stock);
 	stock_pages = READ_ONCE(stock->nr_pages);
@@ -1792,7 +1797,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 		ret = true;
 	}
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 
 	return ret;
 }
@@ -1831,14 +1836,14 @@ static void drain_local_stock(struct work_struct *dummy)
 	 * drain_stock races is that we always operate on local CPU stock
 	 * here with IRQ disabled
 	 */
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	old = drain_obj_stock(stock);
 	drain_stock(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 }
 
@@ -1868,9 +1873,20 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	unsigned long flags;
 
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	if (!localtry_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
+		/*
+		 * In case of unlikely failure to lock percpu stock_lock
+		 * uncharge memcg directly.
+		 */
+		if (mem_cgroup_is_root(memcg))
+			return;
+		page_counter_uncharge(&memcg->memory, nr_pages);
+		if (do_memsw_account())
+			page_counter_uncharge(&memcg->memsw, nr_pages);
+		return;
+	}
 	__refill_stock(memcg, nr_pages);
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 }
 
 /*
@@ -2213,9 +2229,13 @@ int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	unsigned long pflags;
 
 retry:
-	if (consume_stock(memcg, nr_pages))
+	if (consume_stock(memcg, nr_pages, gfp_mask))
 		return 0;
 
+	if (!gfpflags_allow_spinning(gfp_mask))
+		/* Avoid the refill and flush of the older stock */
+		batch = nr_pages;
+
 	if (!do_memsw_account() ||
 	    page_counter_try_charge(&memcg->memsw, batch, &counter)) {
 		if (page_counter_try_charge(&memcg->memory, batch, &counter))
@@ -2699,7 +2719,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 	unsigned long flags;
 	int *bytes;
 
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
 	stock = this_cpu_ptr(&memcg_stock);
 
 	/*
@@ -2752,7 +2772,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 	if (nr)
 		__mod_objcg_mlstate(objcg, pgdat, idx, nr);
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 }
 
@@ -2762,7 +2782,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
 	unsigned long flags;
 	bool ret = false;
 
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
@@ -2770,7 +2790,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
 		ret = true;
 	}
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 
 	return ret;
 }
@@ -2862,7 +2882,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	unsigned long flags;
 	unsigned int nr_pages = 0;
 
-	local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
@@ -2880,7 +2900,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 		stock->nr_bytes &= (PAGE_SIZE - 1);
 	}
 
-	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 
 	if (nr_pages)
-- 
2.43.5

[PATCH bpf-next v8 5/6] mm, bpf: Use memcg in try_alloc_pages().

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Unconditionally use __GFP_ACCOUNT in try_alloc_pages().
The caller is responsible to setup memcg correctly.
All BPF memory accounting is memcg based.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 mm/page_alloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3fbcbeb7de8e..c8068fd2da42 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7189,7 +7189,8 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 	 * specify it here to highlight that try_alloc_pages()
 	 * doesn't want to deplete reserves.
 	 */
-	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC;
+	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC
+			| __GFP_ACCOUNT;
 	unsigned int alloc_flags = ALLOC_TRYLOCK;
 	struct alloc_context ac = { };
 	struct page *page;
@@ -7233,6 +7234,11 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 
 	/* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */
 
+	if (memcg_kmem_online() && page &&
+	    unlikely(__memcg_kmem_charge_page(page, alloc_gfp, order) != 0)) {
+		free_pages_nolock(page, order);
+		page = NULL;
+	}
 	trace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);
 	kmsan_alloc_page(page, order, alloc_gfp);
 	return page;
-- 
2.43.5

[PATCH bpf-next v8 6/6] bpf: Use try_alloc_pages() to allocate pages for bpf needs.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Use try_alloc_pages() and free_pages_nolock() for BPF needs
when context doesn't allow using normal alloc_pages.
This is a prerequisite for further work.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/bpf.h  |  2 +-
 kernel/bpf/arena.c   |  5 ++---
 kernel/bpf/syscall.c | 23 ++++++++++++++++++++---
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f3f50e29d639..e1838a341817 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2348,7 +2348,7 @@ int  generic_map_delete_batch(struct bpf_map *map,
 struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
 struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
 
-int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
+int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
 			unsigned long nr_pages, struct page **page_array);
 #ifdef CONFIG_MEMCG
 void *bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags,
diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 0975d7f22544..8ecc62e6b1a2 100644
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -287,7 +287,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
 		return VM_FAULT_SIGSEGV;
 
 	/* Account into memcg of the process that created bpf_arena */
-	ret = bpf_map_alloc_pages(map, GFP_KERNEL | __GFP_ZERO, NUMA_NO_NODE, 1, &page);
+	ret = bpf_map_alloc_pages(map, NUMA_NO_NODE, 1, &page);
 	if (ret) {
 		range_tree_set(&arena->rt, vmf->pgoff, 1);
 		return VM_FAULT_SIGSEGV;
@@ -465,8 +465,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
 	if (ret)
 		goto out_free_pages;
 
-	ret = bpf_map_alloc_pages(&arena->map, GFP_KERNEL | __GFP_ZERO,
-				  node_id, page_cnt, pages);
+	ret = bpf_map_alloc_pages(&arena->map, node_id, page_cnt, pages);
 	if (ret)
 		goto out;
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c420edbfb7c8..a7af8d0185d0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -569,7 +569,24 @@ static void bpf_map_release_memcg(struct bpf_map *map)
 }
 #endif
 
-int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
+static bool can_alloc_pages(void)
+{
+	return preempt_count() == 0 && !irqs_disabled() &&
+		!IS_ENABLED(CONFIG_PREEMPT_RT);
+}
+
+static struct page *__bpf_alloc_page(int nid)
+{
+	if (!can_alloc_pages())
+		return try_alloc_pages(nid, 0);
+
+	return alloc_pages_node(nid,
+				GFP_KERNEL | __GFP_ZERO | __GFP_ACCOUNT
+				| __GFP_NOWARN,
+				0);
+}
+
+int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
 			unsigned long nr_pages, struct page **pages)
 {
 	unsigned long i, j;
@@ -582,14 +599,14 @@ int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
 	old_memcg = set_active_memcg(memcg);
 #endif
 	for (i = 0; i < nr_pages; i++) {
-		pg = alloc_pages_node(nid, gfp | __GFP_ACCOUNT, 0);
+		pg = __bpf_alloc_page(nid);
 
 		if (pg) {
 			pages[i] = pg;
 			continue;
 		}
 		for (j = 0; j < i; j++)
-			__free_page(pages[j]);
+			free_pages_nolock(pages[j], 0);
 		ret = -ENOMEM;
 		break;
 	}
-- 
2.43.5

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka]

On 2/13/25 04:35, Alexei Starovoitov wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> critical section, but it doesn't prevent NMI, so the fully reentrant
> code cannot use local_lock_irqsave() for exclusive access.
> 
> Introduce localtry_lock_t and localtry_lock_irqsave() that
> disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> from NMI attempting to acquire the same lock will return false.
> 
> In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> Map localtry_lock_irqsave() to preemptible spin_trylock().
> When in hard IRQ or NMI return false right away, since
> spin_trylock() is not safe due to PI issues.
> 
> Note there is no need to use local_inc for acquired variable,
> since it's a percpu variable with strict nesting scopes.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  include/linux/local_lock.h          |  59 +++++++++++++
>  include/linux/local_lock_internal.h | 123 ++++++++++++++++++++++++++++
>  2 files changed, 182 insertions(+)
> 
> diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
> index 091dc0b6bdfb..05c254a5d7d3 100644
> --- a/include/linux/local_lock.h
> +++ b/include/linux/local_lock.h
> @@ -51,6 +51,65 @@
>  #define local_unlock_irqrestore(lock, flags)			\
>  	__local_unlock_irqrestore(lock, flags)
>  
> +/**
> + * localtry_lock_init - Runtime initialize a lock instance
> + */
> +#define localtry_lock_init(lock)		__localtry_lock_init(lock)
> +
> +/**
> + * localtry_lock - Acquire a per CPU local lock
> + * @lock:	The lock variable
> + */
> +#define localtry_lock(lock)		__localtry_lock(lock)
> +
> +/**
> + * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts
> + * @lock:	The lock variable
> + */
> +#define localtry_lock_irq(lock)		__localtry_lock_irq(lock)
> +
> +/**
> + * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable
> + *			 interrupts
> + * @lock:	The lock variable
> + * @flags:	Storage for interrupt flags
> + */
> +#define localtry_lock_irqsave(lock, flags)				\
> +	__localtry_lock_irqsave(lock, flags)
> +
> +/**
> + * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
> + *			      interrupts if acquired
> + * @lock:	The lock variable
> + * @flags:	Storage for interrupt flags
> + *
> + * The function can be used in any context such as NMI or HARDIRQ. Due to
> + * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT.

The "always fail" applies only to the NMI and HARDIRQ contexts, right? It's
not entirely obvious so it sounds worse than it is.

> +
> +#define __localtry_trylock_irqsave(lock, flags)			\
> +	({							\
> +		int __locked;					\
> +								\
> +		typecheck(unsigned long, flags);		\
> +		flags = 0;					\
> +		if (in_nmi() | in_hardirq()) {			\
> +			__locked = 0;				\

Because of this, IIUC?

> +		} else {					\
> +			migrate_disable();			\
> +			__locked = spin_trylock(this_cpu_ptr((lock)));	\
> +			if (!__locked)				\
> +				migrate_enable();		\
> +		}						\
> +		__locked;					\
> +	})
> +
>  #endif /* CONFIG_PREEMPT_RT */

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Alexei Starovoitov]

On Thu, Feb 13, 2025 at 7:04 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 2/13/25 04:35, Alexei Starovoitov wrote:
> > From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> >
> > In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> > critical section, but it doesn't prevent NMI, so the fully reentrant
> > code cannot use local_lock_irqsave() for exclusive access.
> >
> > Introduce localtry_lock_t and localtry_lock_irqsave() that
> > disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> > from NMI attempting to acquire the same lock will return false.
> >
> > In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> > Map localtry_lock_irqsave() to preemptible spin_trylock().
> > When in hard IRQ or NMI return false right away, since
> > spin_trylock() is not safe due to PI issues.
> >
> > Note there is no need to use local_inc for acquired variable,
> > since it's a percpu variable with strict nesting scopes.
> >
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > ---
> >  include/linux/local_lock.h          |  59 +++++++++++++
> >  include/linux/local_lock_internal.h | 123 ++++++++++++++++++++++++++++
> >  2 files changed, 182 insertions(+)
> >
> > diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
> > index 091dc0b6bdfb..05c254a5d7d3 100644
> > --- a/include/linux/local_lock.h
> > +++ b/include/linux/local_lock.h
> > @@ -51,6 +51,65 @@
> >  #define local_unlock_irqrestore(lock, flags)                 \
> >       __local_unlock_irqrestore(lock, flags)
> >
> > +/**
> > + * localtry_lock_init - Runtime initialize a lock instance
> > + */
> > +#define localtry_lock_init(lock)             __localtry_lock_init(lock)
> > +
> > +/**
> > + * localtry_lock - Acquire a per CPU local lock
> > + * @lock:    The lock variable
> > + */
> > +#define localtry_lock(lock)          __localtry_lock(lock)
> > +
> > +/**
> > + * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts
> > + * @lock:    The lock variable
> > + */
> > +#define localtry_lock_irq(lock)              __localtry_lock_irq(lock)
> > +
> > +/**
> > + * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable
> > + *                    interrupts
> > + * @lock:    The lock variable
> > + * @flags:   Storage for interrupt flags
> > + */
> > +#define localtry_lock_irqsave(lock, flags)                           \
> > +     __localtry_lock_irqsave(lock, flags)
> > +
> > +/**
> > + * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
> > + *                         interrupts if acquired
> > + * @lock:    The lock variable
> > + * @flags:   Storage for interrupt flags
> > + *
> > + * The function can be used in any context such as NMI or HARDIRQ. Due to
> > + * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT.
>
> The "always fail" applies only to the NMI and HARDIRQ contexts, right? It's
> not entirely obvious so it sounds worse than it is.
>
> > +
> > +#define __localtry_trylock_irqsave(lock, flags)                      \
> > +     ({                                                      \
> > +             int __locked;                                   \
> > +                                                             \
> > +             typecheck(unsigned long, flags);                \
> > +             flags = 0;                                      \
> > +             if (in_nmi() | in_hardirq()) {                  \
> > +                     __locked = 0;                           \
>
> Because of this, IIUC?

Right.
It's part of commit log:
+ In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
+ Map localtry_lock_irqsave() to preemptible spin_trylock().
+ When in hard IRQ or NMI return false right away, since
+ spin_trylock() is not safe due to PI issues.

Steven explained it in detail in some earlier thread.

realtime is hard. bpf and realtime together are even harder.
Things got much better over the years, but plenty of work ahead.
I can go in detail, but offtopic for this thread.

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Steven Rostedt]

On Thu, 13 Feb 2025 07:23:01 -0800
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> realtime is hard. bpf and realtime together are even harder.

Going for an LWN Quote-of-the-week ? ;-)

-- Steve

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka]

On 2/13/25 04:35, Alexei Starovoitov wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> critical section, but it doesn't prevent NMI, so the fully reentrant
> code cannot use local_lock_irqsave() for exclusive access.
> 
> Introduce localtry_lock_t and localtry_lock_irqsave() that
> disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> from NMI attempting to acquire the same lock will return false.
> 
> In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> Map localtry_lock_irqsave() to preemptible spin_trylock().
> When in hard IRQ or NMI return false right away, since
> spin_trylock() is not safe due to PI issues.
> 
> Note there is no need to use local_inc for acquired variable,
> since it's a percpu variable with strict nesting scopes.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

>  
> +/* localtry_lock_t variants */
> +
> +#define __localtry_lock_init(lock)				\
> +do {								\
> +	__local_lock_init(&(lock)->llock);			\
> +	WRITE_ONCE(&(lock)->acquired, 0);			\

This needs to be WRITE_ONCE((lock)->acquired, 0);

I'm adopting this implementation for my next slab sheaves RFC. But I'll want
localtry_trylock() without _irqsave too, so I've added it locally. Posting
below with the init fix and making the PREEMPT_RT comment clear. Feel free
to fold everything, it would make it easier for me. Or just the fixes, if
you don't want code you don't use yourself.

----8<----
From c4f47afa3d06367d8d54662d6c3a76d3ab6e349d Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Thu, 13 Feb 2025 19:38:31 +0100
Subject: [PATCH] locking/local_lock: add localtry_trylock()

Add a localtry_trylock() variant without _irqsave that will be used in
slab sheaves implementation. Thanks to only disabling preemption and not
irqs, it has a lower overhead. It's not necessary to disable irqs to
avoid a deadlock if the irq context uses trylock and can handle
failures.

Also make the comment of localtry_trylock_irqsave() more clear, and fix a
compilation failure in localtry_lock_init().

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/local_lock.h          | 13 +++++++++++-
 include/linux/local_lock_internal.h | 31 +++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 05c254a5d7d3..1a0bc35839e3 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -77,6 +77,16 @@
 #define localtry_lock_irqsave(lock, flags)				\
 	__localtry_lock_irqsave(lock, flags)
 
+/**
+ * localtry_trylock - Try to acquire a per CPU local lock.
+ * @lock:	The lock variable
+ *
+ * The function can be used in any context such as NMI or HARDIRQ. Due to
+ * locking constrains it will _always_ fail to acquire the lock in NMI or
+ * HARDIRQ context on PREEMPT_RT.
+ */
+#define localtry_trylock(lock)		__localtry_trylock(lock)
+
 /**
  * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
  *			      interrupts if acquired
@@ -84,7 +94,8 @@
  * @flags:	Storage for interrupt flags
  *
  * The function can be used in any context such as NMI or HARDIRQ. Due to
- * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT.
+ * locking constrains it will _always_ fail to acquire the lock in NMI or
+ * HARDIRQ context on PREEMPT_RT.
  */
 #define localtry_trylock_irqsave(lock, flags)				\
 	__localtry_trylock_irqsave(lock, flags)
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index c1369b300777..67bd13d142fa 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -137,7 +137,7 @@ do {								\
 #define __localtry_lock_init(lock)				\
 do {								\
 	__local_lock_init(&(lock)->llock);			\
-	WRITE_ONCE(&(lock)->acquired, 0);			\
+	WRITE_ONCE((lock)->acquired, 0);			\
 } while (0)
 
 #define __localtry_lock(lock)					\
@@ -167,6 +167,24 @@ do {								\
 		WRITE_ONCE(lt->acquired, 1);			\
 	} while (0)
 
+#define __localtry_trylock(lock)				\
+	({							\
+		localtry_lock_t *lt;				\
+		bool _ret;					\
+								\
+		preempt_disable();				\
+		lt = this_cpu_ptr(lock);			\
+		if (!READ_ONCE(lt->acquired)) {			\
+			WRITE_ONCE(lt->acquired, 1);		\
+			local_trylock_acquire(&lt->llock);	\
+			_ret = true;				\
+		} else {					\
+			_ret = false;				\
+			preempt_enable();			\
+		}						\
+		_ret;						\
+	})
+
 #define __localtry_trylock_irqsave(lock, flags)			\
 	({							\
 		localtry_lock_t *lt;				\
@@ -275,12 +293,10 @@ do {								\
 #define __localtry_unlock_irq(lock)			__local_unlock(lock)
 #define __localtry_unlock_irqrestore(lock, flags)	__local_unlock_irqrestore(lock, flags)
 
-#define __localtry_trylock_irqsave(lock, flags)			\
+#define __localtry_trylock(lock)				\
 	({							\
 		int __locked;					\
 								\
-		typecheck(unsigned long, flags);		\
-		flags = 0;					\
 		if (in_nmi() | in_hardirq()) {			\
 			__locked = 0;				\
 		} else {					\
@@ -292,4 +308,11 @@ do {								\
 		__locked;					\
 	})
 
+#define __localtry_trylock_irqsave(lock, flags)			\
+	({							\
+		typecheck(unsigned long, flags);		\
+		flags = 0;					\
+		__localtry_trylock(lock);			\
+	})
+
 #endif /* CONFIG_PREEMPT_RT */
-- 
2.48.1

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka]

On 2/13/25 16:23, Alexei Starovoitov wrote:
> On Thu, Feb 13, 2025 at 7:04 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>>
>>
>> > +
>> > +#define __localtry_trylock_irqsave(lock, flags)                      \
>> > +     ({                                                      \
>> > +             int __locked;                                   \
>> > +                                                             \
>> > +             typecheck(unsigned long, flags);                \
>> > +             flags = 0;                                      \
>> > +             if (in_nmi() | in_hardirq()) {                  \
>> > +                     __locked = 0;                           \
>>
>> Because of this, IIUC?
> 
> Right.
> It's part of commit log:
> + In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> + Map localtry_lock_irqsave() to preemptible spin_trylock().
> + When in hard IRQ or NMI return false right away, since
> + spin_trylock() is not safe due to PI issues.
> 
> Steven explained it in detail in some earlier thread.
> 
> realtime is hard. bpf and realtime together are even harder.
> Things got much better over the years, but plenty of work ahead.
> I can go in detail, but offtopic for this thread.

Thanks, it's fine. Just that the comment of the function could be more clear
then, so people don't have to check implementation/commit log/lore
discussions :)

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Alexei Starovoitov]

On Fri, Feb 14, 2025 at 4:11 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 2/13/25 04:35, Alexei Starovoitov wrote:
> > From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> >
> > In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> > critical section, but it doesn't prevent NMI, so the fully reentrant
> > code cannot use local_lock_irqsave() for exclusive access.
> >
> > Introduce localtry_lock_t and localtry_lock_irqsave() that
> > disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> > from NMI attempting to acquire the same lock will return false.
> >
> > In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> > Map localtry_lock_irqsave() to preemptible spin_trylock().
> > When in hard IRQ or NMI return false right away, since
> > spin_trylock() is not safe due to PI issues.
> >
> > Note there is no need to use local_inc for acquired variable,
> > since it's a percpu variable with strict nesting scopes.
> >
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
>
> ...
>
> >
> > +/* localtry_lock_t variants */
> > +
> > +#define __localtry_lock_init(lock)                           \
> > +do {                                                         \
> > +     __local_lock_init(&(lock)->llock);                      \
> > +     WRITE_ONCE(&(lock)->acquired, 0);                       \
>
> This needs to be WRITE_ONCE((lock)->acquired, 0);

Thanks. Good catch.

> I'm adopting this implementation for my next slab sheaves RFC. But I'll want
> localtry_trylock() without _irqsave too, so I've added it locally. Posting
> below with the init fix and making the PREEMPT_RT comment clear. Feel free
> to fold everything, it would make it easier for me. Or just the fixes, if
> you don't want code you don't use yourself.

+1

> ----8<----
> From c4f47afa3d06367d8d54662d6c3a76d3ab6e349d Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Thu, 13 Feb 2025 19:38:31 +0100
> Subject: [PATCH] locking/local_lock: add localtry_trylock()
>
> Add a localtry_trylock() variant without _irqsave that will be used in
> slab sheaves implementation. Thanks to only disabling preemption and not
> irqs, it has a lower overhead. It's not necessary to disable irqs to
> avoid a deadlock if the irq context uses trylock and can handle
> failures.
>
> Also make the comment of localtry_trylock_irqsave() more clear, and fix a
> compilation failure in localtry_lock_init().
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  include/linux/local_lock.h          | 13 +++++++++++-
>  include/linux/local_lock_internal.h | 31 +++++++++++++++++++++++++----
>  2 files changed, 39 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
> index 05c254a5d7d3..1a0bc35839e3 100644
> --- a/include/linux/local_lock.h
> +++ b/include/linux/local_lock.h
> @@ -77,6 +77,16 @@
>  #define localtry_lock_irqsave(lock, flags)                             \
>         __localtry_lock_irqsave(lock, flags)
>
> +/**
> + * localtry_trylock - Try to acquire a per CPU local lock.
> + * @lock:      The lock variable
> + *
> + * The function can be used in any context such as NMI or HARDIRQ. Due to
> + * locking constrains it will _always_ fail to acquire the lock in NMI or
> + * HARDIRQ context on PREEMPT_RT.
> + */
> +#define localtry_trylock(lock)         __localtry_trylock(lock)
> +
>  /**
>   * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
>   *                           interrupts if acquired
> @@ -84,7 +94,8 @@
>   * @flags:     Storage for interrupt flags
>   *
>   * The function can be used in any context such as NMI or HARDIRQ. Due to
> - * locking constrains it will _always_ fail to acquire the lock on PREEMPT_RT.
> + * locking constrains it will _always_ fail to acquire the lock in NMI or
> + * HARDIRQ context on PREEMPT_RT.

+1 as well.

>   */
>  #define localtry_trylock_irqsave(lock, flags)                          \
>         __localtry_trylock_irqsave(lock, flags)
> diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
> index c1369b300777..67bd13d142fa 100644
> --- a/include/linux/local_lock_internal.h
> +++ b/include/linux/local_lock_internal.h
> @@ -137,7 +137,7 @@ do {                                                                \
>  #define __localtry_lock_init(lock)                             \
>  do {                                                           \
>         __local_lock_init(&(lock)->llock);                      \
> -       WRITE_ONCE(&(lock)->acquired, 0);                       \
> +       WRITE_ONCE((lock)->acquired, 0);                        \
>  } while (0)
>
>  #define __localtry_lock(lock)                                  \
> @@ -167,6 +167,24 @@ do {                                                               \
>                 WRITE_ONCE(lt->acquired, 1);                    \
>         } while (0)
>
> +#define __localtry_trylock(lock)                               \
> +       ({                                                      \
> +               localtry_lock_t *lt;                            \
> +               bool _ret;                                      \
> +                                                               \
> +               preempt_disable();                              \
> +               lt = this_cpu_ptr(lock);                        \
> +               if (!READ_ONCE(lt->acquired)) {                 \
> +                       WRITE_ONCE(lt->acquired, 1);            \
> +                       local_trylock_acquire(&lt->llock);      \
> +                       _ret = true;                            \
> +               } else {                                        \
> +                       _ret = false;                           \
> +                       preempt_enable();                       \
> +               }                                               \
> +               _ret;                                           \
> +       })
> +
>  #define __localtry_trylock_irqsave(lock, flags)                        \
>         ({                                                      \
>                 localtry_lock_t *lt;                            \
> @@ -275,12 +293,10 @@ do {                                                              \
>  #define __localtry_unlock_irq(lock)                    __local_unlock(lock)
>  #define __localtry_unlock_irqrestore(lock, flags)      __local_unlock_irqrestore(lock, flags)
>
> -#define __localtry_trylock_irqsave(lock, flags)                        \
> +#define __localtry_trylock(lock)                               \
>         ({                                                      \
>                 int __locked;                                   \
>                                                                 \
> -               typecheck(unsigned long, flags);                \
> -               flags = 0;                                      \
>                 if (in_nmi() | in_hardirq()) {                  \
>                         __locked = 0;                           \
>                 } else {                                        \
> @@ -292,4 +308,11 @@ do {                                                               \
>                 __locked;                                       \
>         })
>
> +#define __localtry_trylock_irqsave(lock, flags)                        \
> +       ({                                                      \
> +               typecheck(unsigned long, flags);                \
> +               flags = 0;                                      \
> +               __localtry_trylock(lock);                       \
> +       })
> +

All makes sense to me.

Since respin is needed, I can fold the above fix/feature and
push it into a branch with stable sha-s that we both can
use as a base ?

Or you can push just this one patch into a stable branch and I can pull it
and apply the rest on top.

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka]

On 2/14/25 19:32, Alexei Starovoitov wrote:
>>         ({                                                      \
>>                 localtry_lock_t *lt;                            \
>> @@ -275,12 +293,10 @@ do {                                                              \
>>  #define __localtry_unlock_irq(lock)                    __local_unlock(lock)
>>  #define __localtry_unlock_irqrestore(lock, flags)      __local_unlock_irqrestore(lock, flags)
>>
>> -#define __localtry_trylock_irqsave(lock, flags)                        \
>> +#define __localtry_trylock(lock)                               \
>>         ({                                                      \
>>                 int __locked;                                   \
>>                                                                 \
>> -               typecheck(unsigned long, flags);                \
>> -               flags = 0;                                      \
>>                 if (in_nmi() | in_hardirq()) {                  \
>>                         __locked = 0;                           \
>>                 } else {                                        \
>> @@ -292,4 +308,11 @@ do {                                                               \
>>                 __locked;                                       \
>>         })
>>
>> +#define __localtry_trylock_irqsave(lock, flags)                        \
>> +       ({                                                      \
>> +               typecheck(unsigned long, flags);                \
>> +               flags = 0;                                      \
>> +               __localtry_trylock(lock);                       \
>> +       })
>> +
> 
> All makes sense to me.
> 
> Since respin is needed, I can fold the above fix/feature and
> push it into a branch with stable sha-s that we both can
> use as a base ?

I doubt sheaves will be included in 6.15 so it's fine enough for me if you
fold this and perhaps order the result as patch 1?

> Or you can push just this one patch into a stable branch and I can pull it
> and apply the rest on top.

Ideally we'd have PeterZ blessing before we get to stable commit id's...

Thanks.

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Sebastian Sewior]

On 2025-02-14 19:48:57 [+0100], Vlastimil Babka wrote:
> > Since respin is needed, I can fold the above fix/feature and
> > push it into a branch with stable sha-s that we both can
> > use as a base ?
> 
> I doubt sheaves will be included in 6.15 so it's fine enough for me if you
> fold this and perhaps order the result as patch 1?
> 
> > Or you can push just this one patch into a stable branch and I can pull it
> > and apply the rest on top.
> 
> Ideally we'd have PeterZ blessing before we get to stable commit id's...

Yes. As noted in the other thread, I'm all fine with the propose
changes.

> Thanks.

Sebastian

Re: [PATCH bpf-next v8 3/6] locking/local_lock: Introduce localtry_lock_t

[Vlastimil Babka]

On 2/13/25 04:35, Alexei Starovoitov wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> critical section, but it doesn't prevent NMI, so the fully reentrant
> code cannot use local_lock_irqsave() for exclusive access.
> 
> Introduce localtry_lock_t and localtry_lock_irqsave() that
> disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> from NMI attempting to acquire the same lock will return false.
> 
> In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> Map localtry_lock_irqsave() to preemptible spin_trylock().
> When in hard IRQ or NMI return false right away, since
> spin_trylock() is not safe due to PI issues.
> 
> Note there is no need to use local_inc for acquired variable,
> since it's a percpu variable with strict nesting scopes.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

I'm not the maintainer of this area, but with the fixes/addition I proposed,
and having use for this lock variant myself, I think it's fair to add, fwiw:

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.

Re: [PATCH bpf-next v8 6/6] bpf: Use try_alloc_pages() to allocate pages for bpf needs.

[Vlastimil Babka]

On 2/13/25 04:35, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> Use try_alloc_pages() and free_pages_nolock() for BPF needs
> when context doesn't allow using normal alloc_pages.
> This is a prerequisite for further work.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  include/linux/bpf.h  |  2 +-
>  kernel/bpf/arena.c   |  5 ++---
>  kernel/bpf/syscall.c | 23 ++++++++++++++++++++---
>  3 files changed, 23 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f3f50e29d639..e1838a341817 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2348,7 +2348,7 @@ int  generic_map_delete_batch(struct bpf_map *map,
>  struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
>  struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
>  
> -int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
> +int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
>  			unsigned long nr_pages, struct page **page_array);
>  #ifdef CONFIG_MEMCG
>  void *bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags,
> diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> index 0975d7f22544..8ecc62e6b1a2 100644
> --- a/kernel/bpf/arena.c
> +++ b/kernel/bpf/arena.c
> @@ -287,7 +287,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
>  		return VM_FAULT_SIGSEGV;
>  
>  	/* Account into memcg of the process that created bpf_arena */
> -	ret = bpf_map_alloc_pages(map, GFP_KERNEL | __GFP_ZERO, NUMA_NO_NODE, 1, &page);
> +	ret = bpf_map_alloc_pages(map, NUMA_NO_NODE, 1, &page);
>  	if (ret) {
>  		range_tree_set(&arena->rt, vmf->pgoff, 1);
>  		return VM_FAULT_SIGSEGV;
> @@ -465,8 +465,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
>  	if (ret)
>  		goto out_free_pages;
>  
> -	ret = bpf_map_alloc_pages(&arena->map, GFP_KERNEL | __GFP_ZERO,
> -				  node_id, page_cnt, pages);
> +	ret = bpf_map_alloc_pages(&arena->map, node_id, page_cnt, pages);
>  	if (ret)
>  		goto out;
>  
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index c420edbfb7c8..a7af8d0185d0 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -569,7 +569,24 @@ static void bpf_map_release_memcg(struct bpf_map *map)
>  }
>  #endif
>  
> -int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
> +static bool can_alloc_pages(void)
> +{
> +	return preempt_count() == 0 && !irqs_disabled() &&
> +		!IS_ENABLED(CONFIG_PREEMPT_RT);
> +}
> +

I see this is new since v6 and wasn't yet discussed (or I missed it?)

I wonder how reliable these preempt/irq_disabled checks are for correctness
purposes, e.g. we don't have CONFIG_PREEMPT_COUNT enabled always? As longs
as the callers of bpf_map_alloc_pages() know the context and pass gfp
accordingly, can't we use i.e. gfpflags_allow_blocking() to determine if
try_alloc_pages() should be used or not?

> +static struct page *__bpf_alloc_page(int nid)
> +{
> +	if (!can_alloc_pages())
> +		return try_alloc_pages(nid, 0);
> +
> +	return alloc_pages_node(nid,
> +				GFP_KERNEL | __GFP_ZERO | __GFP_ACCOUNT
> +				| __GFP_NOWARN,
> +				0);
> +}
> +
> +int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
>  			unsigned long nr_pages, struct page **pages)
>  {
>  	unsigned long i, j;
> @@ -582,14 +599,14 @@ int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
>  	old_memcg = set_active_memcg(memcg);
>  #endif
>  	for (i = 0; i < nr_pages; i++) {
> -		pg = alloc_pages_node(nid, gfp | __GFP_ACCOUNT, 0);
> +		pg = __bpf_alloc_page(nid);
>  
>  		if (pg) {
>  			pages[i] = pg;
>  			continue;
>  		}
>  		for (j = 0; j < i; j++)
> -			__free_page(pages[j]);
> +			free_pages_nolock(pages[j], 0);
>  		ret = -ENOMEM;
>  		break;
>  	}

Re: [PATCH bpf-next v8 6/6] bpf: Use try_alloc_pages() to allocate pages for bpf needs.

[Alexei Starovoitov]

On Tue, Feb 18, 2025 at 7:36 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 2/13/25 04:35, Alexei Starovoitov wrote:
> > From: Alexei Starovoitov <ast@kernel.org>
> >
> > Use try_alloc_pages() and free_pages_nolock() for BPF needs
> > when context doesn't allow using normal alloc_pages.
> > This is a prerequisite for further work.
> >
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > ---
> >  include/linux/bpf.h  |  2 +-
> >  kernel/bpf/arena.c   |  5 ++---
> >  kernel/bpf/syscall.c | 23 ++++++++++++++++++++---
> >  3 files changed, 23 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index f3f50e29d639..e1838a341817 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -2348,7 +2348,7 @@ int  generic_map_delete_batch(struct bpf_map *map,
> >  struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
> >  struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
> >
> > -int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
> > +int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
> >                       unsigned long nr_pages, struct page **page_array);
> >  #ifdef CONFIG_MEMCG
> >  void *bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags,
> > diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> > index 0975d7f22544..8ecc62e6b1a2 100644
> > --- a/kernel/bpf/arena.c
> > +++ b/kernel/bpf/arena.c
> > @@ -287,7 +287,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
> >               return VM_FAULT_SIGSEGV;
> >
> >       /* Account into memcg of the process that created bpf_arena */
> > -     ret = bpf_map_alloc_pages(map, GFP_KERNEL | __GFP_ZERO, NUMA_NO_NODE, 1, &page);
> > +     ret = bpf_map_alloc_pages(map, NUMA_NO_NODE, 1, &page);
> >       if (ret) {
> >               range_tree_set(&arena->rt, vmf->pgoff, 1);
> >               return VM_FAULT_SIGSEGV;
> > @@ -465,8 +465,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
> >       if (ret)
> >               goto out_free_pages;
> >
> > -     ret = bpf_map_alloc_pages(&arena->map, GFP_KERNEL | __GFP_ZERO,
> > -                               node_id, page_cnt, pages);
> > +     ret = bpf_map_alloc_pages(&arena->map, node_id, page_cnt, pages);
> >       if (ret)
> >               goto out;
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index c420edbfb7c8..a7af8d0185d0 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -569,7 +569,24 @@ static void bpf_map_release_memcg(struct bpf_map *map)
> >  }
> >  #endif
> >
> > -int bpf_map_alloc_pages(const struct bpf_map *map, gfp_t gfp, int nid,
> > +static bool can_alloc_pages(void)
> > +{
> > +     return preempt_count() == 0 && !irqs_disabled() &&
> > +             !IS_ENABLED(CONFIG_PREEMPT_RT);
> > +}
> > +
>
> I see this is new since v6 and wasn't yet discussed (or I missed it?)

It was in v1:
https://lore.kernel.org/bpf/20241116014854.55141-1-alexei.starovoitov@gmail.com/
See Peter's comments.
In this version I open coded preemptible(), since it's more accurate
and disabled the detection on PREEMPT_RT.

> I wonder how reliable these preempt/irq_disabled checks are for correctness
> purposes, e.g. we don't have CONFIG_PREEMPT_COUNT enabled always?

I believe the above doesn't produce false positives.
It's not exhaustive and might change as we learn more and tune it.
Hence I moved it to be bpf specific to iterate quickly instead of
being in inux/gfp.h and also considering Sebastian's comment
that normal kernel code should better know the calling context.

> As longs
> as the callers of bpf_map_alloc_pages() know the context and pass gfp
> accordingly, can't we use i.e. gfpflags_allow_blocking() to determine if
> try_alloc_pages() should be used or not?

bpf infra has a very coarse knowledge of the context.
There are two categories: sleepable or not.
In sleepable GFP_KERNEL is allowed, but it's very narrow and
represents a tiny slice of use cases compared to
non-sleepable. The try_alloc_pages() is for the latter.
netconsole has a similar problem/challenge.
It doesn't know the context where it will be called.
Currently it's just doing GFP_ATOMIC and praying.
This is something to fix eventually when slab is taught about
gfpflags_allow_blocking.