From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:44323)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1bjjXv-0005Fw-Tv
	for qemu-devel@nongnu.org; Tue, 13 Sep 2016 04:58:29 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1bjjXr-0006BB-0U
	for qemu-devel@nongnu.org; Tue, 13 Sep 2016 04:58:27 -0400
Date: Tue, 13 Sep 2016 16:58:19 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20160913085819.GA22052@lemon>
References: <1473326931-9699-1-git-send-email-famz@redhat.com>
	<20160913083914.GA2710@stefanha-x1.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160913083914.GA2710@stefanha-x1.localdomain>
Subject: Re: [Qemu-devel] [PATCH] iothread: Stop threads before main() quits
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, qemu-stable@nongnu.org

On Tue, 09/13 09:39, Stefan Hajnoczi wrote:
> On Thu, Sep 08, 2016 at 05:28:51PM +0800, Fam Zheng wrote:
> > Right after main_loop ends, we release various things but keep iothread
> > alive. The latter is not prepared to the sudden change of resources.
> > 
> > Specifically, after bdrv_close_all(), virtio-scsi dataplane get a
> > surprise at the empty BlockBackend:
> > 
> > (gdb) bt
> >     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:543
> >     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:577
> > 
> > It is because the d->conf.blk->root is set to NULL, then
> > blk_get_aio_context() returns qemu_aio_context, whereas s->ctx is still
> > pointing to the iothread:
> > 
> >     hw/scsi/virtio-scsi.c:543:
> > 
> >     if (s->dataplane_started) {
> >         assert(blk_get_aio_context(d->conf.blk) == s->ctx);
> >     }
> > 
> > To fix this, let's stop iothreads before doing bdrv_close_all().
> 
> Did you consider blk_add_remove_bs_notifier()?  It gets called during
> bdrv_close_all() and would let virtio-scsi survive any other case where
> the same thing happens.

There is already another case (eject):

https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg02243.html

And I don't know how to fix it with blk_add_remove_bs_notifier. Could you
elaborate?

Fam