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FAILED: patch "[PATCH] bpf: Disable preemption in bpf_get_stackid" failed to apply to 6.18-stable tree

PATCH New [email protected] 2 participants 6 messages Sep 3 – Sep 8

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Stable branch BPF BPF tracing
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author maintainer
#0 lore raw

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 15f1bd8574662f1b7b26aaa2e23ebf4066f0117d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090347-bodacious-studio-93ee@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 15f1bd8574662f1b7b26aaa2e23ebf4066f0117d Mon Sep 17 00:00:00 2001
From: Jiri Olsa <[email protected]>
Date: Mon, 3 Aug 2026 23:01:42 +0200
Subject: [PATCH] bpf: Disable preemption in bpf_get_stackid

The get_perf_callchain call needs disabled preemption plus we need it disabled as long as we access its returned trace entries buffer.

Note the bpf_get_stackid_pe function is executed already with preemption disabled.

Fixes d5a3b1f69186 ("bpf: introduce BPF_MAP_TYPE_STACK_TRACE")
Reported-by Tao Chen <[email protected]>
Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Cc [email protected]
Link https://lore.kernel.org/bpf/[email protected] open here
Closes https://lore.kernel.org/bpf/[email protected]/ open here
kernel/bpf/stackmap.c +13 -11
index 3ee0034daf52..5b18d728f4b8 100644
@@ -632,20 +632,22 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 		return -EINVAL;
 
 	max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
-	trace = get_perf_callchain(regs, kernel, user, max_depth,
-				   false, false, 0);
 
-	if (unlikely(!trace))
-		/* couldn't fetch the stack trace */
-		return -EFAULT;
+	scoped_guard(preempt) {
+		trace = get_perf_callchain(regs, kernel, user, max_depth,
+					   false, false, 0);
+		if (unlikely(!trace))
+			/* couldn't fetch the stack trace */
+			return -EFAULT;
 
-	err = stackid_fastpath(&stackid, map, trace, flags);
-	if (err != -ENOENT)
-		return err;
+		err = stackid_fastpath(&stackid, map, trace, flags);
+		if (err != -ENOENT)
+			return err;
 
-	new_bucket = stackid_new_bucket(&stackid, map);
-	if (!new_bucket)
-		return -ENOMEM;
+		new_bucket = stackid_new_bucket(&stackid, map);
+		if (!new_bucket)
+			return -ENOMEM;
+	}
 
 	return stackid_install(&stackid, map, new_bucket, flags);
 }
maintainer
#1 lore raw

PATCH 1/5 bpf: Factor stackid_init function from __bpf_get_stackid

From: Jiri Olsa <[email protected]>

[ Upstream commit 15b837759a97237d647962f9943afe0d55af615a ]

The new stackid_init function stores all the necessary bits for stackid trace and it will be used by other functions in following changes.

Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Link https://lore.kernel.org/bpf/[email protected] open here

Stable-dep-of: 15f1bd857466 ("bpf: Disable preemption in bpf_get_stackid")

Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/stackmap.c | 95 +++++++++++++++++++++++++++----------------
 1 file changed, 59 insertions(+), 36 deletions(-)
kernel/bpf/stackmap.c +59 -36
index 13f4f696a7c04..db64199dbd6fb 100644
@@ -246,33 +246,54 @@ get_callchain_entry_for_task(struct task_struct *task, u32 max_depth)
 #endif
 }
 
-static long __bpf_get_stackid(struct bpf_map *map,
-			      struct perf_callchain_entry *trace, u64 flags)
+struct stackid {
+	struct stack_map_bucket *bucket;
+	u64 *ips;
+	u32  nr;
+	u32  len;
+	u32  hash;
+	u32  id;
+};
+
+static int stackid_init(struct stackid *stackid, struct bpf_map *map,
+			struct perf_callchain_entry *trace, u64 flags)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
-	struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
-	u32 hash, id, trace_nr, trace_len, i, max_depth;
 	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
-	bool user = flags & BPF_F_USER_STACK;
-	u64 *ips;
-	bool hash_matches;
+	u32 max_depth;
 
 	if (trace->nr <= skip)
 		/* skipping more than usable stack trace */
 		return -EFAULT;
 
 	max_depth = stack_map_calculate_max_depth(map->value_size, stack_map_data_size(map), flags);
-	trace_nr = min_t(u32, trace->nr - skip, max_depth - skip);
-	trace_len = trace_nr * sizeof(u64);
-	ips = trace->ip + skip;
-	hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
-	id = hash & (smap->n_buckets - 1);
-	bucket = READ_ONCE(smap->buckets[id]);
+	stackid->nr = min_t(u32, trace->nr - skip, max_depth - skip);
+	stackid->len = stackid->nr * sizeof(u64);
+	stackid->ips = trace->ip + skip;
+	stackid->hash = jhash2((u32 *)stackid->ips, stackid->len / sizeof(u32), 0);
+	stackid->id = stackid->hash & (smap->n_buckets - 1);
+	stackid->bucket = READ_ONCE(smap->buckets[stackid->id]);
+	return 0;
+}
 
-	hash_matches = bucket && bucket->hash == hash;
+static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
+			      struct perf_callchain_entry *trace, u64 flags)
+{
+	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
+	struct stack_map_bucket *new_bucket, *old_bucket;
+	bool user = flags & BPF_F_USER_STACK;
+	bool hash_matches;
+	u32 trace_len, i;
+	int err;
+
+	err = stackid_init(stackid, map, trace, flags);
+	if (err)
+		return err;
+
+	hash_matches = stackid->bucket && stackid->bucket->hash == stackid->hash;
 	/* fast cmp */
 	if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
-		return id;
+		return stackid->id;
 
 	if (stack_map_use_build_id(map)) {
 		struct bpf_stack_build_id *id_offs;

@@ -282,42 +303,42 @@ static long __bpf_get_stackid(struct bpf_map *map,
 			pcpu_freelist_pop(&smap->freelist);
 		if (unlikely(!new_bucket))
 			return -ENOMEM;
-		new_bucket->nr = trace_nr;
+		new_bucket->nr = stackid->nr;
 		id_offs = (struct bpf_stack_build_id *)new_bucket->data;
-		for (i = 0; i < trace_nr; i++)
-			id_offs[i].ip = ips[i];
-		stack_map_get_build_id_offset(id_offs, trace_nr, user, false /* !may_fault */);
-		trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
-		if (hash_matches && bucket->nr == trace_nr &&
-		    memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
+		for (i = 0; i < stackid->nr; i++)
+			id_offs[i].ip = stackid->ips[i];
+		stack_map_get_build_id_offset(id_offs, stackid->nr, user, false /* !may_fault */);
+		trace_len = stackid->nr * sizeof(struct bpf_stack_build_id);
+		if (hash_matches && stackid->bucket->nr == stackid->nr &&
+		    memcmp(stackid->bucket->data, new_bucket->data, trace_len) == 0) {
 			pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
-			return id;
+			return stackid->id;
 		}
-		if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
+		if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID)) {
 			pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 			return -EEXIST;
 		}
 	} else {
-		if (hash_matches && bucket->nr == trace_nr &&
-		    memcmp(bucket->data, ips, trace_len) == 0)
-			return id;
-		if (bucket && !(flags & BPF_F_REUSE_STACKID))
+		if (hash_matches && stackid->bucket->nr == stackid->nr &&
+		    memcmp(stackid->bucket->data, stackid->ips, stackid->len) == 0)
+			return stackid->id;
+		if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID))
 			return -EEXIST;
 
 		new_bucket = (struct stack_map_bucket *)
 			pcpu_freelist_pop(&smap->freelist);
 		if (unlikely(!new_bucket))
 			return -ENOMEM;
-		memcpy(new_bucket->data, ips, trace_len);
+		memcpy(new_bucket->data, stackid->ips, stackid->len);
 	}
 
-	new_bucket->hash = hash;
-	new_bucket->nr = trace_nr;
+	new_bucket->hash = stackid->hash;
+	new_bucket->nr = stackid->nr;
 
-	old_bucket = xchg(&smap->buckets[id], new_bucket);
+	old_bucket = xchg(&smap->buckets[stackid->id], new_bucket);
 	if (old_bucket)
 		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
-	return id;
+	return stackid->id;
 }
 
 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,

@@ -326,6 +347,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 	u32 elem_size = stack_map_data_size(map);
 	bool user = flags & BPF_F_USER_STACK;
 	struct perf_callchain_entry *trace;
+	struct stackid stackid;
 	bool kernel = !user;
 	u32 max_depth;
 

@@ -341,7 +363,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 		/* couldn't fetch the stack trace */
 		return -EFAULT;
 
-	return __bpf_get_stackid(map, trace, flags);
+	return __bpf_get_stackid(&stackid, map, trace, flags);
 }
 
 const struct bpf_func_proto bpf_get_stackid_proto = {

@@ -370,6 +392,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 {
 	struct perf_event *event = ctx->event;
 	struct perf_callchain_entry *trace;
+	struct stackid stackid;
 	bool kernel, user;
 	__u64 nr_kernel;
 	int ret;

@@ -395,7 +418,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 
 	if (kernel) {
 		trace->nr = nr_kernel;
-		ret = __bpf_get_stackid(map, trace, flags);
+		ret = __bpf_get_stackid(&stackid, map, trace, flags);
 	} else { /* user */
 		u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
 

@@ -404,7 +427,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 			return -EFAULT;
 
 		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
-		ret = __bpf_get_stackid(map, trace, flags);
+		ret = __bpf_get_stackid(&stackid, map, trace, flags);
 	}
 
 	/* restore nr */
Signature · 1 line
2.53.0
maintainer
#2 lore raw

PATCH 2/5 bpf: Factor stackid_fastpath function from __bpf_get_stackid

From: Jiri Olsa <[email protected]>

[ Upstream commit 0ca56befcffec3a6c9d1842eae06c74e1cf41f11 ]

The new stackid_fastpath does the fast stack hash and trace check, that does not need new bucket allocation. It covers both just-ip and buildid code paths.

Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Link https://lore.kernel.org/bpf/[email protected] open here

Stable-dep-of: 15f1bd857466 ("bpf: Disable preemption in bpf_get_stackid")

Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/stackmap.c | 43 ++++++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 15 deletions(-)
kernel/bpf/stackmap.c +28 -15
index db64199dbd6fb..b3661d6f18676 100644
@@ -253,6 +253,7 @@ struct stackid {
 	u32  len;
 	u32  hash;
 	u32  id;
+	bool hash_matches;
 };
 
 static int stackid_init(struct stackid *stackid, struct bpf_map *map,

@@ -273,28 +274,46 @@ static int stackid_init(struct stackid *stackid, struct bpf_map *map,
 	stackid->hash = jhash2((u32 *)stackid->ips, stackid->len / sizeof(u32), 0);
 	stackid->id = stackid->hash & (smap->n_buckets - 1);
 	stackid->bucket = READ_ONCE(smap->buckets[stackid->id]);
+	stackid->hash_matches = stackid->bucket && stackid->bucket->hash == stackid->hash;
 	return 0;
 }
 
+static int stackid_fastpath(struct stackid *stackid, struct bpf_map *map,
+			    struct perf_callchain_entry *trace, u64 flags)
+{
+	int err;
+
+	err = stackid_init(stackid, map, trace, flags);
+	if (err)
+		return err;
+
+	/* fast cmp */
+	if (stackid->hash_matches && flags & BPF_F_FAST_STACK_CMP)
+		return stackid->id;
+
+	if (stack_map_use_build_id(map))
+		return -ENOENT;
+	if (stackid->hash_matches && stackid->bucket->nr == stackid->nr &&
+	    memcmp(stackid->bucket->data, stackid->ips, stackid->len) == 0)
+		return stackid->id;
+	if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID))
+		return -EEXIST;
+	return -ENOENT;
+}
+
 static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			      struct perf_callchain_entry *trace, u64 flags)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 	struct stack_map_bucket *new_bucket, *old_bucket;
 	bool user = flags & BPF_F_USER_STACK;
-	bool hash_matches;
 	u32 trace_len, i;
 	int err;
 
-	err = stackid_init(stackid, map, trace, flags);
-	if (err)
+	err = stackid_fastpath(stackid, map, trace, flags);
+	if (err != -ENOENT)
 		return err;
 
-	hash_matches = stackid->bucket && stackid->bucket->hash == stackid->hash;
-	/* fast cmp */
-	if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
-		return stackid->id;
-
 	if (stack_map_use_build_id(map)) {
 		struct bpf_stack_build_id *id_offs;
 

@@ -309,7 +328,7 @@ static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			id_offs[i].ip = stackid->ips[i];
 		stack_map_get_build_id_offset(id_offs, stackid->nr, user, false /* !may_fault */);
 		trace_len = stackid->nr * sizeof(struct bpf_stack_build_id);
-		if (hash_matches && stackid->bucket->nr == stackid->nr &&
+		if (stackid->hash_matches && stackid->bucket->nr == stackid->nr &&
 		    memcmp(stackid->bucket->data, new_bucket->data, trace_len) == 0) {
 			pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 			return stackid->id;

@@ -319,12 +338,6 @@ static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			return -EEXIST;
 		}
 	} else {
-		if (hash_matches && stackid->bucket->nr == stackid->nr &&
-		    memcmp(stackid->bucket->data, stackid->ips, stackid->len) == 0)
-			return stackid->id;
-		if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID))
-			return -EEXIST;
-
 		new_bucket = (struct stack_map_bucket *)
 			pcpu_freelist_pop(&smap->freelist);
 		if (unlikely(!new_bucket))
Signature · 1 line
2.53.0
maintainer
#3 lore raw

PATCH 3/5 bpf: Factor stackid_new_bucket from __bpf_get_stackid

In reply to Sasha Levin

From: Jiri Olsa <[email protected]>

[ Upstream commit bb4e6f4e1b68fe60c04ca04c564c6624e837dbf4 ]

The new stackid_new_bucket allocates the new bucket and initializes it with the trace data.

Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Link https://lore.kernel.org/bpf/[email protected] open here

Stable-dep-of: 15f1bd857466 ("bpf: Disable preemption in bpf_get_stackid")

Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/stackmap.c | 48 +++++++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 18 deletions(-)
kernel/bpf/stackmap.c +30 -18
index b3661d6f18676..cd3b91a726336 100644
@@ -301,31 +301,52 @@ static int stackid_fastpath(struct stackid *stackid, struct bpf_map *map,
 	return -ENOENT;
 }
 
+static struct stack_map_bucket *
+stackid_new_bucket(struct stackid *stackid, struct bpf_map *map)
+{
+	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
+	struct bpf_stack_build_id *id_offs;
+	struct stack_map_bucket *bucket;
+	u32 i;
+
+	bucket = (struct stack_map_bucket *) pcpu_freelist_pop(&smap->freelist);
+	if (unlikely(!bucket))
+		return NULL;
+
+	if (stack_map_use_build_id(map)) {
+		id_offs = (struct bpf_stack_build_id *)bucket->data;
+		for (i = 0; i < stackid->nr; i++)
+			id_offs[i].ip = stackid->ips[i];
+	} else {
+		memcpy(bucket->data, stackid->ips, stackid->len);
+	}
+
+	bucket->hash = stackid->hash;
+	bucket->nr = stackid->nr;
+	return bucket;
+}
+
 static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			      struct perf_callchain_entry *trace, u64 flags)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 	struct stack_map_bucket *new_bucket, *old_bucket;
 	bool user = flags & BPF_F_USER_STACK;
-	u32 trace_len, i;
+	u32 trace_len;
 	int err;
 
 	err = stackid_fastpath(stackid, map, trace, flags);
 	if (err != -ENOENT)
 		return err;
 
+	new_bucket = stackid_new_bucket(stackid, map);
+	if (!new_bucket)
+		return -ENOMEM;
+
 	if (stack_map_use_build_id(map)) {
 		struct bpf_stack_build_id *id_offs;
 
-		/* for build_id+offset, pop a bucket before slow cmp */
-		new_bucket = (struct stack_map_bucket *)
-			pcpu_freelist_pop(&smap->freelist);
-		if (unlikely(!new_bucket))
-			return -ENOMEM;
-		new_bucket->nr = stackid->nr;
 		id_offs = (struct bpf_stack_build_id *)new_bucket->data;
-		for (i = 0; i < stackid->nr; i++)
-			id_offs[i].ip = stackid->ips[i];
 		stack_map_get_build_id_offset(id_offs, stackid->nr, user, false /* !may_fault */);
 		trace_len = stackid->nr * sizeof(struct bpf_stack_build_id);
 		if (stackid->hash_matches && stackid->bucket->nr == stackid->nr &&

@@ -337,17 +358,8 @@ static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 			return -EEXIST;
 		}
-	} else {
-		new_bucket = (struct stack_map_bucket *)
-			pcpu_freelist_pop(&smap->freelist);
-		if (unlikely(!new_bucket))
-			return -ENOMEM;
-		memcpy(new_bucket->data, stackid->ips, stackid->len);
 	}
 
-	new_bucket->hash = stackid->hash;
-	new_bucket->nr = stackid->nr;
-
 	old_bucket = xchg(&smap->buckets[stackid->id], new_bucket);
 	if (old_bucket)
 		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
Signature · 1 line
2.53.0
maintainer
#4 lore raw

PATCH 4/5 bpf: Use stack id functions instead of __bpf_get_stackid

In reply to Sasha Levin

From: Jiri Olsa <[email protected]>

[ Upstream commit 09b3fd6caa0b57f8a39254ee5db3af30bdd53c18 ]

Replacing __bpf_get_stackid calls with sequence of following functions:

stackid_fastpath
stackid_new_bucket
stackid_install

This makes code more structured and allows us to easily disable preemption only in bpf_get_stackid in following changes.

Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Link https://lore.kernel.org/bpf/[email protected] open here

Stable-dep-of: 15f1bd857466 ("bpf: Disable preemption in bpf_get_stackid")

Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/stackmap.c | 43 +++++++++++++++++++++++++++----------------
 1 file changed, 27 insertions(+), 16 deletions(-)
kernel/bpf/stackmap.c +27 -16
index cd3b91a726336..0634eaae48702 100644
@@ -326,22 +326,13 @@ stackid_new_bucket(struct stackid *stackid, struct bpf_map *map)
 	return bucket;
 }
 
-static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
-			      struct perf_callchain_entry *trace, u64 flags)
+static long stackid_install(struct stackid *stackid, struct bpf_map *map,
+			    struct stack_map_bucket *new_bucket, u64 flags)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
-	struct stack_map_bucket *new_bucket, *old_bucket;
 	bool user = flags & BPF_F_USER_STACK;
+	struct stack_map_bucket *old_bucket;
 	u32 trace_len;
-	int err;
-
-	err = stackid_fastpath(stackid, map, trace, flags);
-	if (err != -ENOENT)
-		return err;
-
-	new_bucket = stackid_new_bucket(stackid, map);
-	if (!new_bucket)
-		return -ENOMEM;
 
 	if (stack_map_use_build_id(map)) {
 		struct bpf_stack_build_id *id_offs;

@@ -371,10 +362,12 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 {
 	u32 elem_size = stack_map_data_size(map);
 	bool user = flags & BPF_F_USER_STACK;
+	struct stack_map_bucket *new_bucket;
 	struct perf_callchain_entry *trace;
 	struct stackid stackid;
 	bool kernel = !user;
 	u32 max_depth;
+	int err;
 
 	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))

@@ -388,7 +381,15 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 		/* couldn't fetch the stack trace */
 		return -EFAULT;
 
-	return __bpf_get_stackid(&stackid, map, trace, flags);
+	err = stackid_fastpath(&stackid, map, trace, flags);
+	if (err != -ENOENT)
+		return err;
+
+	new_bucket = stackid_new_bucket(&stackid, map);
+	if (!new_bucket)
+		return -ENOMEM;
+
+	return stackid_install(&stackid, map, new_bucket, flags);
 }
 
 const struct bpf_func_proto bpf_get_stackid_proto = {

@@ -416,6 +417,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 	   struct bpf_map *, map, u64, flags)
 {
 	struct perf_event *event = ctx->event;
+	struct stack_map_bucket *new_bucket;
 	struct perf_callchain_entry *trace;
 	struct stackid stackid;
 	bool kernel, user;

@@ -443,7 +445,6 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 
 	if (kernel) {
 		trace->nr = nr_kernel;
-		ret = __bpf_get_stackid(&stackid, map, trace, flags);
 	} else { /* user */
 		u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
 

@@ -452,12 +453,22 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 			return -EFAULT;
 
 		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
-		ret = __bpf_get_stackid(&stackid, map, trace, flags);
 	}
 
+	ret = stackid_fastpath(&stackid, map, trace, flags);
+	if (ret != -ENOENT)
+		goto out;
+
+	new_bucket = stackid_new_bucket(&stackid, map);
+	if (new_bucket) {
+		trace->nr = nr;
+		return stackid_install(&stackid, map, new_bucket, flags);
+	}
+	ret = -ENOMEM;
+
+out:
 	/* restore nr */
 	trace->nr = nr;
-
 	return ret;
 }
Signature · 1 line
2.53.0
maintainer
#5 lore raw

PATCH 5/5 bpf: Disable preemption in bpf_get_stackid

In reply to Sasha Levin

From: Jiri Olsa <[email protected]>

[ Upstream commit 15f1bd8574662f1b7b26aaa2e23ebf4066f0117d ]

The get_perf_callchain call needs disabled preemption plus we need it disabled as long as we access its returned trace entries buffer.

Note the bpf_get_stackid_pe function is executed already with preemption disabled.

Fixes d5a3b1f69186 ("bpf: introduce BPF_MAP_TYPE_STACK_TRACE")
Reported-by Tao Chen <[email protected]>
Signed-off-by Jiri Olsa <[email protected]>
Signed-off-by Andrii Nakryiko <[email protected]>
Cc [email protected]
Link https://lore.kernel.org/bpf/[email protected] open here
Closes https://lore.kernel.org/bpf/[email protected]/ open here
[ adapted get_perf_callchain() to the older six-argument form ]
Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/stackmap.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)
kernel/bpf/stackmap.c +13 -11
index 0634eaae48702..49ef03ab0595a 100644
@@ -374,20 +374,22 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 		return -EINVAL;
 
 	max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
-	trace = get_perf_callchain(regs, kernel, user, max_depth,
-				   false, false);
 
-	if (unlikely(!trace))
-		/* couldn't fetch the stack trace */
-		return -EFAULT;
+	scoped_guard(preempt) {
+		trace = get_perf_callchain(regs, kernel, user, max_depth,
+					   false, false);
+		if (unlikely(!trace))
+			/* couldn't fetch the stack trace */
+			return -EFAULT;
 
-	err = stackid_fastpath(&stackid, map, trace, flags);
-	if (err != -ENOENT)
-		return err;
+		err = stackid_fastpath(&stackid, map, trace, flags);
+		if (err != -ENOENT)
+			return err;
 
-	new_bucket = stackid_new_bucket(&stackid, map);
-	if (!new_bucket)
-		return -ENOMEM;
+		new_bucket = stackid_new_bucket(&stackid, map);
+		if (!new_bucket)
+			return -ENOMEM;
+	}
 
 	return stackid_install(&stackid, map, new_bucket, flags);
 }
Signature · 1 line
2.53.0