From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56319) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1co6tL-00085h-F7 for qemu-devel@nongnu.org; Wed, 15 Mar 2017 07:14:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1co6tJ-0006ts-OZ for qemu-devel@nongnu.org; Wed, 15 Mar 2017 07:14:54 -0400 Date: Wed, 15 Mar 2017 19:14:45 +0800 From: Fam Zheng Message-ID: <20170315111445.GE3088@lemon.lan> References: <20170314171120.80741-1-vsementsov@virtuozzo.com> <20170315110351.GG4030@noname.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170315110351.GG4030@noname.str.redhat.com> Subject: Re: [Qemu-devel] [PATCH] blk: fix aio context loss on media change List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, den@openvz.org, jsnow@redhat.com On Wed, 03/15 12:03, Kevin Wolf wrote: > Am 14.03.2017 um 18:11 hat Vladimir Sementsov-Ogievskiy geschrieben: > > If we have separate iothread for cdrom, we lose connection to it on > > qmp_blockdev_change_medium, as aio_context is on bds which is dropped > > and switched with new one. > > > > As an example result, after such media change we have crash on > > virtio_scsi_ctx_check: Assertion `blk_get_aio_context(d->conf.blk) == s->ctx' failed. > > > > Signed-off-by: Vladimir Sementsov-Ogievskiy > > --- > > > > Hi all! > > > > We've faced into this assert, and there some kind of fix. I don't sure that > > such fix doesn't break some conceptions, in this case, I hope, someone will > > propose a true-way solution. > > The "true way" would be proper AioContext management in the sense that > all users of a BDS can specify a specific AioContext that they need and > if they all agree, callbacks are invoked to change everyone to that > AioContext. If they conflict, attaching the new user would have to error > out. > > But we discussed this earlier, and while I'm not completely sure any > more about the details, I seem to remeber that Paolo said something > along the lines that AioContext is going away anyway and building the > code for proper management would be wasted time. Matches my impression. > > Stefan, Paolo, do you remember the details why we didn't even do a > simple fix like the one below? I think there were some patches on the > list, no? ISTM the concern was mostly "what about other BB in the graph?" Should the new op blocker API be used in this one (a new type of perm)? > > Kevin > > > ====== > > Also, on master branch I can't reproduce it as vm crashed earlier, without any > > eject/change, on assert(s->ctx && s->dataplane_started) in > > virtio_scsi_data_plane_handle_ctrl(). It looks like race with > > virtio_scsi_dataplane_start(), and for test (to reproduce assert described above), > > I've "fixed" it with just: > > > > @@ -63,6 +63,7 @@ static bool virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev, > > { > > VirtIOSCSI *s = VIRTIO_SCSI(vdev); > > > > + sleep(10); This will be fixed by https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg02659.html Fam