> On Feb 22, 2021, at 10:21 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > 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.c uses casting in multiple places. How about we fix it in a separate patch? Thanks, Song > >> + 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; > > [...]
