From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44753) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cygGr-00067v-SF for qemu-devel@nongnu.org; Thu, 13 Apr 2017 11:02:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cygGq-00044D-TT for qemu-devel@nongnu.org; Thu, 13 Apr 2017 11:02:53 -0400 Date: Thu, 13 Apr 2017 11:02:39 -0400 From: Jeff Cody Message-ID: <20170413150239.GF15762@localhost.localdomain> References: <20170412204641.GA15762@localhost.localdomain> <20170412222251.GB15762@localhost.localdomain> <20170412235420.GB8607@lemon> <20170413011109.GC15762@localhost.localdomain> <20170413143959.GE13387@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170413143959.GE13387@stefanha-x1.localdomain> Subject: Re: [Qemu-devel] Regression from 2.8: stuck in bdrv_drain() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Paolo Bonzini , Fam Zheng , kwolf@redhat.com, peter.maydell@linaro.org, qemu-block@nongnu.org, qemu-devel@nongnu.org, John Snow On Thu, Apr 13, 2017 at 03:39:59PM +0100, Stefan Hajnoczi wrote: > On Thu, Apr 13, 2017 at 01:45:55PM +0800, Paolo Bonzini wrote: > > > > > > On 13/04/2017 09:11, Jeff Cody wrote: > > >> It didn't make it into 2.9-rc4 because of limited time. :( > > >> > > >> Looks like there is no -rc5, we'll have to document this as a known issue. > > >> Users should "block-job-complete/cancel" as soon as possible to avoid such a > > >> hang. > > > > > > I'd argue for including a fix for 2.9, since this is both a regression, and > > > a hard lock without possible recovery short of restarting the QEMU process. > > > > It is a bit of a corner case (and jobs on I/O thread are relatively rare > > too), so maybe it's not worth delaying 2.9. It has been delayed already > > quite a bit. Another reason I think I prefer to wait is to ensure that > > we have an entry in qemu-iotests to avoid the future regression. > > I also think this does not require delaying the release: > > 1. It needs to be marked as a known issue in the release notes. > 2. Let's roll the 2.9.1 stable release within a month of 2.9.0. > > If both conditions are met then very few end users will be exposed to > the problem. I hope libvirt will create IOThreads by default soon but > for the time being it is not a widely used configuration. > Without the fix, iothreads are not usable in 2.9.0, because a running block job can create a deadlock by a guest-initiated reboot. I think losing the ability to use iothreads is enough reason to warrant a fix (especially if an -rc5 may happen anyway). -Jeff