# Re: \[PATCH v6 bpf-next 2/6\] bpf: prevent deadlock from recursive bpf\_task\_storage\_\[get\|delete\]

- From: Martin KaFai Lau \<hidden\>
- Date: 2021-02-26 00:03:29 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/02/6279558
- Thread: https://ratatoskr.run/bpf/2021/02/6279545/t.md

```text
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 <redacted>
```