On Thu, Feb 25, 2021 at 03:43:15PM -0800, Song Liu 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. 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. Acked-by: Martin KaFai Lau <kafai@xxxxxx>
