diff options
| author | Martin KaFai Lau <martin.lau@kernel.org> | 2022-10-25 11:45:19 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-10-25 23:11:46 -0700 |
| commit | e8b02296a6b8d07de752d6157d863a642117bcd3 (patch) | |
| tree | 4c91db052a526edd1deba8b1c3509bc117345dec /kernel/bpf/bpf_task_storage.c | |
| parent | 6d65500c34d897329ed1be0fd3c4014ec52cd473 (diff) | |
bpf: Avoid taking spinlock in bpf_task_storage_get if potential deadlock is detected
bpf_task_storage_get() does a lookup and optionally inserts
new data if BPF_LOCAL_STORAGE_GET_F_CREATE is present.
During lookup, it will cache the lookup result and caching requires to
acquire a spinlock. When potential deadlock is detected (by the
bpf_task_storage_busy pcpu-counter added in
commit bc235cdb423a ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]")),
the current behavior is returning NULL immediately to avoid deadlock. It is
too pessimistic. This patch will go ahead to do a lookup (which is a
lockless operation) but it will avoid caching it in order to avoid
acquiring the spinlock.
When lookup fails to find the data and BPF_LOCAL_STORAGE_GET_F_CREATE
is set, an insertion is needed and this requires acquiring a spinlock.
This patch will still return NULL when a potential deadlock is detected.
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-5-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/bpf_task_storage.c')
| -rw-r--r-- | kernel/bpf/bpf_task_storage.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c index 2726435e3eda..bc52bc8b59f7 100644 --- a/kernel/bpf/bpf_task_storage.c +++ b/kernel/bpf/bpf_task_storage.c @@ -230,17 +230,17 @@ out: /* Called by bpf_task_storage_get*() helpers */ static void *__bpf_task_storage_get(struct bpf_map *map, struct task_struct *task, void *value, - u64 flags, gfp_t gfp_flags) + u64 flags, gfp_t gfp_flags, bool nobusy) { struct bpf_local_storage_data *sdata; - sdata = task_storage_lookup(task, map, true); + sdata = task_storage_lookup(task, map, nobusy); if (sdata) return sdata->data; /* only allocate new storage, when the task is refcounted */ if (refcount_read(&task->usage) && - (flags & BPF_LOCAL_STORAGE_GET_F_CREATE)) { + (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) && nobusy) { sdata = bpf_local_storage_update( task, (struct bpf_local_storage_map *)map, value, BPF_NOEXIST, gfp_flags); @@ -254,17 +254,18 @@ static void *__bpf_task_storage_get(struct bpf_map *map, BPF_CALL_5(bpf_task_storage_get_recur, struct bpf_map *, map, struct task_struct *, task, void *, value, u64, flags, gfp_t, gfp_flags) { + bool nobusy; void *data; WARN_ON_ONCE(!bpf_rcu_lock_held()); if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task) return (unsigned long)NULL; - if (!bpf_task_storage_trylock()) - return (unsigned long)NULL; + nobusy = bpf_task_storage_trylock(); data = __bpf_task_storage_get(map, task, value, flags, - gfp_flags); - bpf_task_storage_unlock(); + gfp_flags, nobusy); + if (nobusy) + bpf_task_storage_unlock(); return (unsigned long)data; } |