From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50288) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj0Um-0005Cg-PR for qemu-devel@nongnu.org; Thu, 24 Mar 2016 04:19:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aj0Uj-0007nB-JA for qemu-devel@nongnu.org; Thu, 24 Mar 2016 04:19:56 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:45864) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj0Uj-0007my-Cw for qemu-devel@nongnu.org; Thu, 24 Mar 2016 04:19:53 -0400 Received: from localhost by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 24 Mar 2016 02:19:50 -0600 References: <1458123018-18651-1-git-send-email-famz@redhat.com> <1458123018-18651-5-git-send-email-famz@redhat.com> <20160317150057.GP14062@stefanha-x1.localdomain> <56EAC82A.50907@redhat.com> <20160322125254.GB9749@ad.usersys.redhat.com> <56F18955.4060005@redhat.com> <20160323091009.64eb4cd8.cornelia.huck@de.ibm.com> <56F25D23.5070604@redhat.com> <56F25E0B.2000105@de.ibm.com> From: tu bo Message-ID: <56F3A31D.5000609@linux.vnet.ibm.com> Date: Thu, 24 Mar 2016 16:19:41 +0800 MIME-Version: 1.0 In-Reply-To: <56F25E0B.2000105@de.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 4/4] virtio-blk: Clean up start/stop with mutex and BH List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger , Paolo Bonzini , Cornelia Huck Cc: Kevin Wolf , Fam Zheng , qemu-block@nongnu.org, "Michael S. Tsirkin" , Stefan Hajnoczi , qemu-devel@nongnu.org, Stefan Hajnoczi Hi Christian: On 03/23/2016 05:12 PM, Christian Borntraeger wrote: > On 03/23/2016 10:08 AM, Paolo Bonzini wrote: >> >> >> On 23/03/2016 09:10, Cornelia Huck wrote: >>>> - /* Kick right away to begin processing requests already in vring */ >>>> - event_notifier_set(virtio_queue_get_host_notifier(s->vq)); >>>> + vblk->dataplane_started = true; >>>> >>>> - /* Get this show started by hooking up our callbacks */ >>>> + /* Get this show started by hooking up our callbacks. */ >>>> aio_context_acquire(s->ctx); >>>> virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, true, true); >>>> aio_context_release(s->ctx); >>>> + atomic_dec(&s->starting); >>>> + >>>> + /* Kick right away to begin processing requests already in vring */ >>>> + event_notifier_set(virtio_queue_get_host_notifier(s->vq)); >>> >>> I'm wondering whether moving this event_notifier_set() masks something? >>> IOW, may we run into trouble if the event notifier is set from some >>> other path before the callbacks are set up properly? >> >> The reentrancy check should catch that... But: >> >> 1) the patch really makes no difference, your fix is enough for me > > > Tu Bo, can you test with master + Cornelias 6 refactoring patches and nothing on top? With qemu master + Cornelia's 6 refactoring patches and nothing on top, I did NOT see crash so far. > > > >> 2) vblk->dataplane_started becomes true before the callbacks are set; >> that should be enough. >> >> 3) this matches what I tested, but it would of course be better if the >> assertions on s->starting suffice >> >>>> - if (!vblk->dataplane_started || s->stopping) { >>>> + if (!vblk->dataplane_started) { >>> >>> No fear of reentrancy here? >> >> No, because this is only invoked from reset, hence only from the CPU >> thread and only under the BQL. >> >> On start, reentrancy happens between iothread (running outside BQL) and >> a CPU thread (running within BQL). >> >> Paolo >> >>>> return; >>>> } >>>> >>>> @@ -255,7 +251,7 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s) >>>> vblk->dataplane_started = false; >>>> return; >>>> } >>>> - s->stopping = true; >>>> + >>>> trace_virtio_blk_data_plane_stop(s); >>>> >>>> aio_context_acquire(s->ctx); >>>> @@ -274,5 +270,4 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s) >>>> k->set_guest_notifiers(qbus->parent, 1, false); >>>> >>>> vblk->dataplane_started = false; >>>> - s->stopping = false; >>>> } >>>> >>> >> >