Re: [PATCH v2 2/2] vhost-user: add a request-reply lock

[Michael S. Tsirkin]

On Thu, Aug 29, 2024 at 02:45:45PM +0530, Prasad Pandit wrote:
> Hello Michael,
> 
> On Thu, 29 Aug 2024 at 13:12, Michael S. Tsirkin <mst@redhat.com> wrote:
> > Weird.  Seems to indicate some kind of deadlock?
> 
> * Such a deadlock should occur across all environments I guess, not
> sure why it happens selectively. It is strange.

Some kind of race?

> > So maybe vhost_user_postcopy_end should take the BQL?
> ===
> diff --git a/migration/savevm.c b/migration/savevm.c
> index e7c1215671..31acda3818 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2050,7 +2050,9 @@ static void *postcopy_ram_listen_thread(void *opaque)
>           */
>          qemu_event_wait(&mis->main_thread_load_event);
>      }
> +    bql_lock();
>      postcopy_ram_incoming_cleanup(mis);
> +    bql_unlock();
> 
>      if (load_res < 0) {
>          /*
> ===
> 
> * Actually a BQL patch above was tested and it worked fine. But not
> sure if it is an acceptable solution. Another contention was taking
> BQL could make things more complicated, so a local vhost-user specific
> lock should be better.
> 
> ...wdyt?
> ---
>   - Prasad

Keep it simple, is my advice. Not causing regressions is good.

-- 
MST