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Subject: Re: [Qemu-devel] [PATCH] thread-pool: fix deadlock when callbacks
 depends on each other
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To: Paolo Bonzini <pbonzini@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Stefan Hajnoczi <stefanha@gmail.com>

> Good catch!  The main problem with the patch is that you need to use
> atomic_inc/atomic_dec to increment and decrement pool->pending_completions.

Ok.

> Secondarily, event_notifier_set is pretty heavy-weight, does it work if
> you wrap the loop like this?
>
> restart:
>      QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
>          ...
>      }
>      if (pool->pending_completions) {
>          goto restart;
>      }
>      event_notifier_test_and_clear(notifier);
>      if (pool->pending_completions) {
>          event_notifier_set(notifier);
>          goto restart;
>      }

I'll test it tomorrow. I assume you want to avoid calling 
event_notifier_set() until function is reentered via aio_pool?

 > Finally, the same bug is also in block/linux-aio.c and
 > block/win32-aio.c.

I can try with linux-aio, but my knowledge of windows api is zero...

-- 
mg