From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:34175)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1XKgTM-0004ho-G4
	for qemu-devel@nongnu.org; Fri, 22 Aug 2014 00:29:14 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1XKgTG-0003W6-AZ
	for qemu-devel@nongnu.org; Fri, 22 Aug 2014 00:29:08 -0400
Received: from mx1.redhat.com ([209.132.183.28]:44305)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1XKgTG-0003Vv-0q
	for qemu-devel@nongnu.org; Fri, 22 Aug 2014 00:29:02 -0400
Received: from int-mx11.intmail.prod.int.phx2.redhat.com
	(int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24])
	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s7M4T1sU016940
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256
	verify=OK)
	for <qemu-devel@nongnu.org>; Fri, 22 Aug 2014 00:29:01 -0400
Date: Fri, 22 Aug 2014 12:29:17 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20140822042917.GD3410@T430.redhat.com>
References: <1408622216-9578-1-git-send-email-famz@redhat.com>
	<1408622216-9578-7-git-send-email-famz@redhat.com>
	<20140821165244.GE22844@stefanha-thinkpad.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20140821165244.GE22844@stefanha-thinkpad.redhat.com>
Subject: Re: [Qemu-devel] [RFC PATCH 6/9] blkdebug: Implement .cancel_async
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: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org

On Thu, 08/21 17:52, Stefan Hajnoczi wrote:
> On Thu, Aug 21, 2014 at 07:56:53PM +0800, Fam Zheng wrote:
> > @@ -446,12 +439,25 @@ static void error_callback_bh(void *opaque)
> >      qemu_aio_release(acb);
> >  }
> >  
> > +static void blkdebug_aio_cancel_async(BlockDriverAIOCB *blockacb)
> > +{
> > +    BlkdebugAIOCB *acb = container_of(blockacb, BlkdebugAIOCB, common);
> > +    blockacb->cb(blockacb->opaque, -ECANCELED);
> > +    qemu_aio_release(acb);
> > +}
> > +
> >  static void blkdebug_aio_cancel(BlockDriverAIOCB *blockacb)
> >  {
> >      BlkdebugAIOCB *acb = container_of(blockacb, BlkdebugAIOCB, common);
> >      qemu_aio_release(acb);
> >  }
> 
> Both blkdebug_aio_cancel() and blkdebug_aio_cancel_async() look
> incorrect.  It is not safe to release acb because the
> error_callback_bh() BH may still be scheduled.
> 
> I guess we don't hit this problem because the error injection happens
> within the same event loop iteration.  In practice no one ever calls
> blkdebug_aio_cancel()?
> 

I'll drop this patch and send a separate fix for blkdebug_aio_cancel.

Fam