[PATCH bpf-next v4 1/2] bpf: Add lookup_and_delete_elem for BPF_MAP_STACK_TRACE

[PATCH bpf-next v4 1/2] bpf: Add lookup_and_delete_elem for BPF_MAP_STACK_TRACE

[Tao Chen]

The stacktrace map can be easily full, which will lead to failure in
obtaining the stack. In addition to increasing the size of the map,
another solution is to delete the stack_id after looking it up from
the user, so extend the existing bpf_map_lookup_and_delete_elem()
functionality to stacktrace map types.

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 include/linux/bpf.h   |  2 +-
 kernel/bpf/stackmap.c | 16 ++++++++++++++--
 kernel/bpf/syscall.c  |  8 +++++---
 3 files changed, 20 insertions(+), 6 deletions(-)

Change list:
 v1 -> v2:
  - typo s/detele/delete/.(Jiri)
  - make sure following lookup fails after deleting the stack_id with NOENT.(Jiri)
  - use '&key' directly as the update value.(Jiri)
  v1: https://lore.kernel.org/bpf/20250908113622.810652-1-chen.dylane@linux.dev
 v2 -> v3:
  - rename bpf_stackmap_copy_and_delete with bpf_stackmap_extract.(Andrii)
  v2: https://lore.kernel.org/bpf/20250909163223.864120-1-chen.dylane@linux.dev
 v3 -> v4:
  - describe what the test is for in commit message.(Leon)
  - 'val_buf' should stay on a single line.(Leon)
  v3: https://lore.kernel.org/bpf/20250920155211.1354348-1-chen.dylane@linux.dev

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8f6e87f0f3a..9d6f7671ba1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2703,7 +2703,7 @@ int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
 int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 			    u64 flags);
 
-int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value);
+int bpf_stackmap_extract(struct bpf_map *map, void *key, void *value, bool delete);
 
 int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file,
 				 void *key, void *value, u64 map_flags);
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 3615c06b7df..2e182a3ac4c 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -646,7 +646,15 @@ static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
 }
 
 /* Called from syscall */
-int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
+static int stack_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
+					    void *value, u64 flags)
+{
+	return bpf_stackmap_extract(map, key, value, true);
+}
+
+/* Called from syscall */
+int bpf_stackmap_extract(struct bpf_map *map, void *key, void *value,
+			 bool delete)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 	struct stack_map_bucket *bucket, *old_bucket;
@@ -663,7 +671,10 @@ int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 	memcpy(value, bucket->data, trace_len);
 	memset(value + trace_len, 0, map->value_size - trace_len);
 
-	old_bucket = xchg(&smap->buckets[id], bucket);
+	if (delete)
+		old_bucket = bucket;
+	else
+		old_bucket = xchg(&smap->buckets[id], bucket);
 	if (old_bucket)
 		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 	return 0;
@@ -754,6 +765,7 @@ const struct bpf_map_ops stack_trace_map_ops = {
 	.map_free = stack_map_free,
 	.map_get_next_key = stack_map_get_next_key,
 	.map_lookup_elem = stack_map_lookup_elem,
+	.map_lookup_and_delete_elem = stack_map_lookup_and_delete_elem,
 	.map_update_elem = stack_map_update_elem,
 	.map_delete_elem = stack_map_delete_elem,
 	.map_check_btf = map_check_no_btf,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0fbfa8532c3..c380a2576fc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -318,7 +318,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE) {
 		err = bpf_percpu_cgroup_storage_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
-		err = bpf_stackmap_copy(map, key, value);
+		err = bpf_stackmap_extract(map, key, value, false);
 	} else if (IS_FD_ARRAY(map) || IS_FD_PROG_ARRAY(map)) {
 		err = bpf_fd_array_map_lookup_elem(map, key, value);
 	} else if (IS_FD_HASH(map)) {
@@ -1627,7 +1627,8 @@ struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map)
 }
 EXPORT_SYMBOL_GPL(bpf_map_inc_not_zero);
 
-int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
+int __weak bpf_stackmap_extract(struct bpf_map *map, void *key, void *value,
+				bool delete)
 {
 	return -ENOTSUPP;
 }
@@ -2158,7 +2159,8 @@ static int map_lookup_and_delete_elem(union bpf_attr *attr)
 	} else if (map->map_type == BPF_MAP_TYPE_HASH ||
 		   map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
 		   map->map_type == BPF_MAP_TYPE_LRU_HASH ||
-		   map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
+		   map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
+		   map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
 		if (!bpf_map_is_offloaded(map)) {
 			bpf_disable_instrumentation();
 			rcu_read_lock();
-- 
2.48.1

[PATCH bpf-next v4 2/2] selftests/bpf: Add stacktrace map lookup_and_delete_elem test case

[Tao Chen]

Add tests for stacktrace map lookup and delete:
1. use bpf_map_lookup_and_delete_elem to lookup and delete the target
   stack_id,
2. lookup the deleted stack_id again to double check.

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 .../selftests/bpf/prog_tests/stacktrace_map.c | 21 ++++++++++++++++++-
 .../selftests/bpf/progs/test_stacktrace_map.c |  8 +++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
index 84a7e405e91..d50659fc25e 100644
--- a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
+++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
@@ -3,7 +3,7 @@
 
 void test_stacktrace_map(void)
 {
-	int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
+	int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd, stack_key_map_fd;
 	const char *prog_name = "oncpu";
 	int err, prog_fd, stack_trace_len;
 	const char *file = "./test_stacktrace_map.bpf.o";
@@ -11,6 +11,8 @@ void test_stacktrace_map(void)
 	struct bpf_program *prog;
 	struct bpf_object *obj;
 	struct bpf_link *link;
+	__u32 stack_id;
+	char val_buf[PERF_MAX_STACK_DEPTH * sizeof(struct bpf_stack_build_id)];
 
 	err = bpf_prog_test_load(file, BPF_PROG_TYPE_TRACEPOINT, &obj, &prog_fd);
 	if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
@@ -41,6 +43,10 @@ void test_stacktrace_map(void)
 	if (CHECK_FAIL(stack_amap_fd < 0))
 		goto disable_pmu;
 
+	stack_key_map_fd = bpf_find_map(__func__, obj, "stack_key_map");
+	if (CHECK_FAIL(stack_key_map_fd < 0))
+		goto disable_pmu;
+
 	/* give some time for bpf program run */
 	sleep(1);
 
@@ -68,6 +74,19 @@ void test_stacktrace_map(void)
 		  "err %d errno %d\n", err, errno))
 		goto disable_pmu;
 
+	err = bpf_map_lookup_elem(stack_key_map_fd, &key, &stack_id);
+	if (CHECK(err, "stack_key_map lookup", "err %d errno %d\n", err, errno))
+		goto disable_pmu;
+
+	err = bpf_map_lookup_and_delete_elem(stackmap_fd, &stack_id, &val_buf);
+	if (CHECK(err, "stackmap lookup and delete",
+		  "err %d errno %d\n", err, errno))
+		goto disable_pmu;
+
+	err = bpf_map_lookup_elem(stackmap_fd, &stack_id, &val_buf);
+	CHECK((!err || errno != ENOENT), "stackmap lookup deleted stack_id",
+	      "err %d errno %d\n", err, errno);
+
 disable_pmu:
 	bpf_link__destroy(link);
 close_prog:
diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
index 47568007b66..3bede76c151 100644
--- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
+++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
@@ -38,6 +38,13 @@ struct {
 	__type(value, stack_trace_t);
 } stack_amap SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u32);
+} stack_key_map SEC(".maps");
+
 /* taken from /sys/kernel/tracing/events/sched/sched_switch/format */
 struct sched_switch_args {
 	unsigned long long pad;
@@ -64,6 +71,7 @@ int oncpu(struct sched_switch_args *ctx)
 	/* The size of stackmap and stackid_hmap should be the same */
 	key = bpf_get_stackid(ctx, &stackmap, 0);
 	if ((int)key >= 0) {
+		bpf_map_update_elem(&stack_key_map, &val, &key, 0);
 		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
 		stack_p = bpf_map_lookup_elem(&stack_amap, &key);
 		if (stack_p)
-- 
2.48.1

Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add stacktrace map lookup_and_delete_elem test case

[Andrii Nakryiko]

On Mon, Sep 22, 2025 at 7:03 AM Tao Chen <chen.dylane@linux.dev> wrote:
>
> Add tests for stacktrace map lookup and delete:
> 1. use bpf_map_lookup_and_delete_elem to lookup and delete the target
>    stack_id,
> 2. lookup the deleted stack_id again to double check.
>
> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> ---
>  .../selftests/bpf/prog_tests/stacktrace_map.c | 21 ++++++++++++++++++-
>  .../selftests/bpf/progs/test_stacktrace_map.c |  8 +++++++
>  2 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
> index 84a7e405e91..d50659fc25e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
> +++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
> @@ -3,7 +3,7 @@
>
>  void test_stacktrace_map(void)
>  {
> -       int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
> +       int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd, stack_key_map_fd;
>         const char *prog_name = "oncpu";
>         int err, prog_fd, stack_trace_len;
>         const char *file = "./test_stacktrace_map.bpf.o";
> @@ -11,6 +11,8 @@ void test_stacktrace_map(void)
>         struct bpf_program *prog;
>         struct bpf_object *obj;
>         struct bpf_link *link;
> +       __u32 stack_id;
> +       char val_buf[PERF_MAX_STACK_DEPTH * sizeof(struct bpf_stack_build_id)];
>
>         err = bpf_prog_test_load(file, BPF_PROG_TYPE_TRACEPOINT, &obj, &prog_fd);
>         if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
> @@ -41,6 +43,10 @@ void test_stacktrace_map(void)
>         if (CHECK_FAIL(stack_amap_fd < 0))
>                 goto disable_pmu;
>
> +       stack_key_map_fd = bpf_find_map(__func__, obj, "stack_key_map");
> +       if (CHECK_FAIL(stack_key_map_fd < 0))

please don't use CHECK*() macros, they are superseded by more targeted
ASSERT_xxx() ones

pw-bot: cr


> +               goto disable_pmu;
> +
>         /* give some time for bpf program run */
>         sleep(1);
>
> @@ -68,6 +74,19 @@ void test_stacktrace_map(void)
>                   "err %d errno %d\n", err, errno))
>                 goto disable_pmu;
>
> +       err = bpf_map_lookup_elem(stack_key_map_fd, &key, &stack_id);
> +       if (CHECK(err, "stack_key_map lookup", "err %d errno %d\n", err, errno))
> +               goto disable_pmu;
> +
> +       err = bpf_map_lookup_and_delete_elem(stackmap_fd, &stack_id, &val_buf);
> +       if (CHECK(err, "stackmap lookup and delete",
> +                 "err %d errno %d\n", err, errno))
> +               goto disable_pmu;
> +
> +       err = bpf_map_lookup_elem(stackmap_fd, &stack_id, &val_buf);
> +       CHECK((!err || errno != ENOENT), "stackmap lookup deleted stack_id",
> +             "err %d errno %d\n", err, errno);

bpf_map_lookup_elem() returns error code directly, no need to use
errno, just check that err == -ENOENT

> +
>  disable_pmu:
>         bpf_link__destroy(link);
>  close_prog:
> diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> index 47568007b66..3bede76c151 100644
> --- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> +++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> @@ -38,6 +38,13 @@ struct {
>         __type(value, stack_trace_t);
>  } stack_amap SEC(".maps");
>
> +struct {
> +       __uint(type, BPF_MAP_TYPE_ARRAY);
> +       __uint(max_entries, 1);
> +       __type(key, __u32);
> +       __type(value, __u32);
> +} stack_key_map SEC(".maps");
> +
>  /* taken from /sys/kernel/tracing/events/sched/sched_switch/format */
>  struct sched_switch_args {
>         unsigned long long pad;
> @@ -64,6 +71,7 @@ int oncpu(struct sched_switch_args *ctx)
>         /* The size of stackmap and stackid_hmap should be the same */
>         key = bpf_get_stackid(ctx, &stackmap, 0);
>         if ((int)key >= 0) {
> +               bpf_map_update_elem(&stack_key_map, &val, &key, 0);

ugh... you'd just use a global variable if this test was used through
skeleton... maybe convert the test to skeleton and get rid of all
those unnecessary bpf_find_map() calls as well?

>                 bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
>                 stack_p = bpf_map_lookup_elem(&stack_amap, &key);
>                 if (stack_p)
> --
> 2.48.1
>

Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add stacktrace map lookup_and_delete_elem test case

[Tao Chen]

在 2025/9/23 04:58, Andrii Nakryiko 写道:
> On Mon, Sep 22, 2025 at 7:03 AM Tao Chen <chen.dylane@linux.dev> wrote:
>>
>> Add tests for stacktrace map lookup and delete:
>> 1. use bpf_map_lookup_and_delete_elem to lookup and delete the target
>>     stack_id,
>> 2. lookup the deleted stack_id again to double check.
>>
>> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
>> ---
>>   .../selftests/bpf/prog_tests/stacktrace_map.c | 21 ++++++++++++++++++-
>>   .../selftests/bpf/progs/test_stacktrace_map.c |  8 +++++++
>>   2 files changed, 28 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
>> index 84a7e405e91..d50659fc25e 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_map.c
>> @@ -3,7 +3,7 @@
>>
>>   void test_stacktrace_map(void)
>>   {
>> -       int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
>> +       int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd, stack_key_map_fd;
>>          const char *prog_name = "oncpu";
>>          int err, prog_fd, stack_trace_len;
>>          const char *file = "./test_stacktrace_map.bpf.o";
>> @@ -11,6 +11,8 @@ void test_stacktrace_map(void)
>>          struct bpf_program *prog;
>>          struct bpf_object *obj;
>>          struct bpf_link *link;
>> +       __u32 stack_id;
>> +       char val_buf[PERF_MAX_STACK_DEPTH * sizeof(struct bpf_stack_build_id)];
>>
>>          err = bpf_prog_test_load(file, BPF_PROG_TYPE_TRACEPOINT, &obj, &prog_fd);
>>          if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
>> @@ -41,6 +43,10 @@ void test_stacktrace_map(void)
>>          if (CHECK_FAIL(stack_amap_fd < 0))
>>                  goto disable_pmu;
>>
>> +       stack_key_map_fd = bpf_find_map(__func__, obj, "stack_key_map");
>> +       if (CHECK_FAIL(stack_key_map_fd < 0))
> 
> please don't use CHECK*() macros, they are superseded by more targeted
> ASSERT_xxx() ones
> 

got it, thanks.

> pw-bot: cr
> 
> 
>> +               goto disable_pmu;
>> +
>>          /* give some time for bpf program run */
>>          sleep(1);
>>
>> @@ -68,6 +74,19 @@ void test_stacktrace_map(void)
>>                    "err %d errno %d\n", err, errno))
>>                  goto disable_pmu;
>>
>> +       err = bpf_map_lookup_elem(stack_key_map_fd, &key, &stack_id);
>> +       if (CHECK(err, "stack_key_map lookup", "err %d errno %d\n", err, errno))
>> +               goto disable_pmu;
>> +
>> +       err = bpf_map_lookup_and_delete_elem(stackmap_fd, &stack_id, &val_buf);
>> +       if (CHECK(err, "stackmap lookup and delete",
>> +                 "err %d errno %d\n", err, errno))
>> +               goto disable_pmu;
>> +
>> +       err = bpf_map_lookup_elem(stackmap_fd, &stack_id, &val_buf);
>> +       CHECK((!err || errno != ENOENT), "stackmap lookup deleted stack_id",
>> +             "err %d errno %d\n", err, errno);
> 
> bpf_map_lookup_elem() returns error code directly, no need to use
> errno, just check that err == -ENOENT
> 

ok.

>> +
>>   disable_pmu:
>>          bpf_link__destroy(link);
>>   close_prog:
>> diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
>> index 47568007b66..3bede76c151 100644
>> --- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
>> +++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
>> @@ -38,6 +38,13 @@ struct {
>>          __type(value, stack_trace_t);
>>   } stack_amap SEC(".maps");
>>
>> +struct {
>> +       __uint(type, BPF_MAP_TYPE_ARRAY);
>> +       __uint(max_entries, 1);
>> +       __type(key, __u32);
>> +       __type(value, __u32);
>> +} stack_key_map SEC(".maps");
>> +
>>   /* taken from /sys/kernel/tracing/events/sched/sched_switch/format */
>>   struct sched_switch_args {
>>          unsigned long long pad;
>> @@ -64,6 +71,7 @@ int oncpu(struct sched_switch_args *ctx)
>>          /* The size of stackmap and stackid_hmap should be the same */
>>          key = bpf_get_stackid(ctx, &stackmap, 0);
>>          if ((int)key >= 0) {
>> +               bpf_map_update_elem(&stack_key_map, &val, &key, 0);
> 
> ugh... you'd just use a global variable if this test was used through
> skeleton... maybe convert the test to skeleton and get rid of all
> those unnecessary bpf_find_map() calls as well?
> 

Yes, the test case seems too old, i will refactor it with skeleton.
>>                  bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
>>                  stack_p = bpf_map_lookup_elem(&stack_amap, &key);
>>                  if (stack_p)
>> --
>> 2.48.1
>>


-- 
Best Regards
Tao Chen