On 09/27/2018 01:10 AM, Dmitry Vyukov wrote:
>
> Would a stack trace for call_rcu be helpful here? I have this idea for
> a long time, but never get around to implementing it:
> https://bugzilla.kernel.org/show_bug.cgi?id=198437
>
> Also FWIW I recently used the following hack for another net bug. It
> made that other bug involving call_rcu way more likely to fire. Maybe
> it will be helpful here too.
>
> diff --git a/net/core/dst.c b/net/core/dst.c
> index 81ccf20e28265..591a8d0aca545 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -187,8 +187,16 @@ void dst_release(struct dst_entry *dst)
> if (unlikely(newrefcnt < 0))
> net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
> __func__, dst, newrefcnt);
> - if (!newrefcnt)
> - call_rcu(&dst->rcu_head, dst_destroy_rcu);
> + if (!newrefcnt) {
> + if (lock_is_held(&rcu_bh_lock_map) ||
> + lock_is_held(&rcu_lock_map) ||
> + lock_is_held(&rcu_sched_lock_map)) {
> + call_rcu(&dst->rcu_head, dst_destroy_rcu);
> + } else {
> + synchronize_rcu();
dst_release() can be called in context we hold a spinlock, this would be bad to
reschedule here.
> + dst_destroy_rcu(&dst->rcu_head);
> + }
> + }
> }
> }
>
