On Mon, Feb 22, 2021 at 5:23 PM Song Liu <songliubraving@xxxxxx> wrote: > > BPF helpers bpf_task_storage_[get|delete] could hold two locks: > bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling > these helpers from fentry/fexit programs on functions in bpf_*_storage.c > may cause deadlock on either locks. > > Prevent such deadlock with a per cpu counter, bpf_task_storage_busy, which > is similar to bpf_prog_active. We need this counter to be global, because > the two locks here belong to two different objects: bpf_local_storage_map > and bpf_local_storage. If we pick one of them as the owner of the counter, > it is still possible to trigger deadlock on the other lock. For example, > if bpf_local_storage_map owns the counters, it cannot prevent deadlock > on bpf_local_storage->lock when two maps are used. > > Signed-off-by: Song Liu <songliubraving@xxxxxx> > --- > kernel/bpf/bpf_task_storage.c | 57 ++++++++++++++++++++++++++++++----- > 1 file changed, 50 insertions(+), 7 deletions(-) > [...] > @@ -109,7 +136,9 @@ static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key) > goto out; > } > > + bpf_task_storage_lock(); > sdata = task_storage_lookup(task, map, true); > + bpf_task_storage_unlock(); > put_pid(pid); > return sdata ? sdata->data : NULL; > out: > @@ -141,8 +170,10 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key, > goto out; > } > > + bpf_task_storage_lock(); > sdata = bpf_local_storage_update( > task, (struct bpf_local_storage_map *)map, value, map_flags); this should probably be container_of() instead of casting > + bpf_task_storage_unlock(); > > err = PTR_ERR_OR_ZERO(sdata); > out: > @@ -185,7 +216,9 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key) > goto out; > } > > + bpf_task_storage_lock(); > err = task_storage_delete(task, map); > + bpf_task_storage_unlock(); > out: > put_pid(pid); > return err; [...]
