Hi,
On 6/24/2023 11:13 AM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu().
> Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into
> per-cpu free list the _rcu() flavor waits for RCU grace period and then moves
> objects into free_by_rcu_ttrace list where they are waiting for RCU
> task trace grace period to be freed into slab.
SNIP
>
> static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
> @@ -498,8 +566,8 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
>
> static void free_mem_alloc(struct bpf_mem_alloc *ma)
> {
> - /* waiting_for_gp_ttrace lists was drained, but __free_rcu might
> - * still execute. Wait for it now before we freeing percpu caches.
> + /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
> + * might still execute. Wait for them.
> *
> * rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
> * but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
I think an extra rcu_barrier() before rcu_barrier_tasks_trace() is still
needed here, otherwise free_mem_alloc will not wait for inflight
__free_by_rcu() and there will oops in rcu_do_batch().
