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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Prasad Pandit <ppandit@redhat.com>
Cc: qemu-devel@nongnu.org, farosas@suse.de, jasowang@redhat.com,
	mcoqueli@redhat.com, peterx@redhat.com,
	"Prasad Pandit" <pjp@fedoraproject.org>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>
Subject: Re: [PATCH v2 2/2] vhost-user: add a request-reply lock
Date: Thu, 29 Aug 2024 05:21:49 -0400	[thread overview]
Message-ID: <20240829052033-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CAE8KmOzC__Z6wgSv9sGcAPrbbZBOQg7tD=6An-=XZVouPCA2Bg@mail.gmail.com>

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



  reply	other threads:[~2024-08-29  9:22 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-08-28 10:09 [PATCH v2 0/2] Postcopy migration and vhost-user errors Prasad Pandit
2024-08-28 10:09 ` [PATCH v2 1/2] vhost: fail device start if iotlb update fails Prasad Pandit
2024-08-28 10:09 ` [PATCH v2 2/2] vhost-user: add a request-reply lock Prasad Pandit
2024-08-28 11:15   ` Michael S. Tsirkin
2024-08-29  5:39     ` Prasad Pandit
2024-08-29  6:23       ` Michael S. Tsirkin
2024-08-29  7:42   ` Michael S. Tsirkin
2024-08-29  9:15     ` Prasad Pandit
2024-08-29  9:21       ` Michael S. Tsirkin [this message]
2024-08-29 14:29       ` Peter Xu
2024-08-29 15:05         ` Michael S. Tsirkin
2024-08-29 20:29           ` Peter Xu
2024-09-10 17:10 ` [PATCH v2 0/2] Postcopy migration and vhost-user errors Michael S. Tsirkin
2024-09-11  7:14   ` Prasad Pandit
2024-09-11  9:46     ` Michael S. Tsirkin

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