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* [PATCH v2 bpf-next 1/2] bpf: Add open coded version of kmem_cache iterator
@ 2024-10-24  7:48 Namhyung Kim
  2024-10-24  7:48 ` [PATCH v2 bpf-next 2/2] selftests/bpf: Add a test for open coded kmem_cache iter Namhyung Kim
  0 siblings, 1 reply; 5+ messages in thread
From: Namhyung Kim @ 2024-10-24  7:48 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko
  Cc: Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
	John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
	LKML, bpf, Andrew Morton, Christoph Lameter, Pekka Enberg,
	David Rientjes, Joonsoo Kim, Vlastimil Babka, Roman Gushchin,
	Hyeonggon Yoo, linux-mm, Arnaldo Carvalho de Melo, Kees Cook

Add a new open coded iterator for kmem_cache which can be called from a
BPF program like below.  It doesn't take any argument and traverses all
kmem_cache entries.

  struct kmem_cache *pos;

  bpf_for_each(kmem_cache, pos) {
      ...
  }

As it needs to grab slab_mutex, it should be called from sleepable BPF
programs only.

Also update the existing iterator code to use the open coded version
internally as suggested by Andrii.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
v2)
 * prevent restart after the last element  (Martin)
 * update existing code to use the open coded version (Andrii)

 kernel/bpf/helpers.c         |   3 +
 kernel/bpf/kmem_cache_iter.c | 151 +++++++++++++++++++++++++----------
 2 files changed, 110 insertions(+), 44 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5c3fdb29c1b1fe53..ddddb060835bac4b 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3112,6 +3112,9 @@ BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_get_kmem_cache)
+BTF_ID_FLAGS(func, bpf_iter_kmem_cache_new, KF_ITER_NEW | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_iter_kmem_cache_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_iter_kmem_cache_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/kernel/bpf/kmem_cache_iter.c b/kernel/bpf/kmem_cache_iter.c
index ebc101d7da51b57c..3ae2158d767f4526 100644
--- a/kernel/bpf/kmem_cache_iter.c
+++ b/kernel/bpf/kmem_cache_iter.c
@@ -8,16 +8,116 @@
 
 #include "../../mm/slab.h" /* kmem_cache, slab_caches and slab_mutex */
 
+/* open-coded version */
+struct bpf_iter_kmem_cache {
+	__u64 __opaque[1];
+} __attribute__((aligned(8)));
+
+struct bpf_iter_kmem_cache_kern {
+	struct kmem_cache *pos;
+} __attribute__((aligned(8)));
+
+#define KMEM_CACHE_POS_START  ((void *)1L)
+
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it)
+{
+	struct bpf_iter_kmem_cache_kern *kit = (void *)it;
+
+	BUILD_BUG_ON(sizeof(*kit) > sizeof(*it));
+	BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it));
+
+	kit->pos = KMEM_CACHE_POS_START;
+	return 0;
+}
+
+__bpf_kfunc struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it)
+{
+	struct bpf_iter_kmem_cache_kern *kit = (void *)it;
+	struct kmem_cache *prev = kit->pos;
+	struct kmem_cache *next;
+	bool destroy = false;
+
+	if (!prev)
+		return NULL;
+
+	mutex_lock(&slab_mutex);
+
+	if (list_empty(&slab_caches)) {
+		mutex_unlock(&slab_mutex);
+		return NULL;
+	}
+
+	if (prev == KMEM_CACHE_POS_START)
+		next = list_first_entry(&slab_caches, struct kmem_cache, list);
+	else if (list_last_entry(&slab_caches, struct kmem_cache, list) == prev)
+		next = NULL;
+	else
+		next = list_next_entry(prev, list);
+
+	/* boot_caches have negative refcount, don't touch them */
+	if (next && next->refcount > 0)
+		next->refcount++;
+
+	/* Skip kmem_cache_destroy() for active entries */
+	if (prev && prev != KMEM_CACHE_POS_START) {
+		if (prev->refcount > 1)
+			prev->refcount--;
+		else if (prev->refcount == 1)
+			destroy = true;
+	}
+
+	mutex_unlock(&slab_mutex);
+
+	if (destroy)
+		kmem_cache_destroy(prev);
+
+	kit->pos = next;
+	return next;
+}
+
+__bpf_kfunc void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it)
+{
+	struct bpf_iter_kmem_cache_kern *kit = (void *)it;
+	struct kmem_cache *s = kit->pos;
+	bool destroy = false;
+
+	if (s == NULL || s == KMEM_CACHE_POS_START)
+		return;
+
+	mutex_lock(&slab_mutex);
+
+	/* Skip kmem_cache_destroy() for active entries */
+	if (s->refcount > 1)
+		s->refcount--;
+	else if (s->refcount == 1)
+		destroy = true;
+
+	mutex_unlock(&slab_mutex);
+
+	if (destroy)
+		kmem_cache_destroy(s);
+}
+
+__bpf_kfunc_end_defs();
+
 struct bpf_iter__kmem_cache {
 	__bpf_md_ptr(struct bpf_iter_meta *, meta);
 	__bpf_md_ptr(struct kmem_cache *, s);
 };
 
+union kmem_cache_iter_priv {
+	struct bpf_iter_kmem_cache it;
+	struct bpf_iter_kmem_cache_kern kit;
+};
+
 static void *kmem_cache_iter_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	loff_t cnt = 0;
 	bool found = false;
 	struct kmem_cache *s;
+	union kmem_cache_iter_priv *p = seq->private;
 
 	mutex_lock(&slab_mutex);
 
@@ -43,8 +143,9 @@ static void *kmem_cache_iter_seq_start(struct seq_file *seq, loff_t *pos)
 	mutex_unlock(&slab_mutex);
 
 	if (!found)
-		return NULL;
+		s = NULL;
 
+	p->kit.pos = s;
 	return s;
 }
 
@@ -55,63 +156,24 @@ static void kmem_cache_iter_seq_stop(struct seq_file *seq, void *v)
 		.meta = &meta,
 		.s = v,
 	};
+	union kmem_cache_iter_priv *p = seq->private;
 	struct bpf_prog *prog;
-	bool destroy = false;
 
 	meta.seq = seq;
 	prog = bpf_iter_get_info(&meta, true);
 	if (prog && !ctx.s)
 		bpf_iter_run_prog(prog, &ctx);
 
-	if (ctx.s == NULL)
-		return;
-
-	mutex_lock(&slab_mutex);
-
-	/* Skip kmem_cache_destroy() for active entries */
-	if (ctx.s->refcount > 1)
-		ctx.s->refcount--;
-	else if (ctx.s->refcount == 1)
-		destroy = true;
-
-	mutex_unlock(&slab_mutex);
-
-	if (destroy)
-		kmem_cache_destroy(ctx.s);
+	bpf_iter_kmem_cache_destroy(&p->it);
 }
 
 static void *kmem_cache_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct kmem_cache *s = v;
-	struct kmem_cache *next = NULL;
-	bool destroy = false;
+	union kmem_cache_iter_priv *p = seq->private;
 
 	++*pos;
 
-	mutex_lock(&slab_mutex);
-
-	if (list_last_entry(&slab_caches, struct kmem_cache, list) != s) {
-		next = list_next_entry(s, list);
-
-		WARN_ON_ONCE(next->refcount == 0);
-
-		/* boot_caches have negative refcount, don't touch them */
-		if (next->refcount > 0)
-			next->refcount++;
-	}
-
-	/* Skip kmem_cache_destroy() for active entries */
-	if (s->refcount > 1)
-		s->refcount--;
-	else if (s->refcount == 1)
-		destroy = true;
-
-	mutex_unlock(&slab_mutex);
-
-	if (destroy)
-		kmem_cache_destroy(s);
-
-	return next;
+	return bpf_iter_kmem_cache_next(&p->it);
 }
 
 static int kmem_cache_iter_seq_show(struct seq_file *seq, void *v)
@@ -143,6 +205,7 @@ BTF_ID_LIST_GLOBAL_SINGLE(bpf_kmem_cache_btf_id, struct, kmem_cache)
 
 static const struct bpf_iter_seq_info kmem_cache_iter_seq_info = {
 	.seq_ops		= &kmem_cache_iter_seq_ops,
+	.seq_priv_size		= sizeof(union kmem_cache_iter_priv),
 };
 
 static void bpf_iter_kmem_cache_show_fdinfo(const struct bpf_iter_aux_info *aux,
-- 
2.47.0.105.g07ac214952-goog



^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-10-30 21:35 UTC | newest]

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2024-10-24  7:48 [PATCH v2 bpf-next 1/2] bpf: Add open coded version of kmem_cache iterator Namhyung Kim
2024-10-24  7:48 ` [PATCH v2 bpf-next 2/2] selftests/bpf: Add a test for open coded kmem_cache iter Namhyung Kim
2024-10-24 18:08   ` Alexei Starovoitov
2024-10-30  1:40     ` Namhyung Kim
2024-10-30 21:35       ` Namhyung Kim

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