From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AD7EC43461 for ; Mon, 14 Sep 2020 14:38:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 036F6207EA for ; Mon, 14 Sep 2020 14:38:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Vf976JL0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 036F6207EA Authentication-Results: mail.kernel.org; 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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0.0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Mit9XoPEfICDqq/V" Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=stefanha@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/14 00:11:19 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.792, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , fam@euphon.net, qemu-block@nongnu.org, armbru@redhat.com, xiexiangyou@huawei.com, qemu-devel@nongnu.org, pbonzini@redhat.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Mit9XoPEfICDqq/V Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Aug 11, 2020 at 09:54:08PM +0800, Zhenyu Ye wrote: > Hi Kevin, >=20 > On 2020/8/10 23:38, Kevin Wolf wrote: > > Am 10.08.2020 um 16:52 hat Zhenyu Ye geschrieben: > >> Before doing qmp actions, we need to lock the qemu_global_mutex, > >> so the qmp actions should not take too long time. > >> > >> Unfortunately, some qmp actions need to acquire aio context and > >> this may take a long time. The vm will soft lockup if this time > >> is too long. > >=20 > > Do you have a specific situation in mind where getting the lock of an > > AioContext can take a long time? I know that the main thread can > > block for considerable time, but QMP commands run in the main thread, s= o > > this patch doesn't change anything for this case. It would be effective > > if an iothread blocks, but shouldn't everything running in an iothread > > be asynchronous and therefore keep the AioContext lock only for a short > > time? > >=20 >=20 > Theoretically, everything running in an iothread is asynchronous. However= , > some 'asynchronous' actions are not non-blocking entirely, such as > io_submit(). This will block while the iodepth is too big and I/O pressu= re > is too high. If we do some qmp actions, such as 'info block', at this ti= me, > may cause vm soft lockup. This series can make these qmp actions safer. >=20 > I constructed the scene as follow: > 1. create a vm with 4 disks, using iothread. > 2. add press to the CPU on the host. In my scene, the CPU usage exceeds = 95%. > 3. add press to the 4 disks in the vm at the same time. I used the fio a= nd > some parameters are: >=20 > =09 fio -rw=3Drandrw -bs=3D1M -size=3D1G -iodepth=3D512 -ioengine=3Dlibai= o -numjobs=3D4 >=20 > 4. do block query actions, for example, by virsh: >=20 > =09virsh qemu-monitor-command [vm name] --hmp info block >=20 > Then the vm will soft lockup, the calltrace is: >=20 > [ 192.311393] watchdog: BUG: soft lockup - CPU#1 stuck for 42s! [kworker= /1:1:33] Hi, Sorry I haven't had time to investigate this myself yet. Do you also have a QEMU backtrace when the hang occurs? Let's find out if QEMU is stuck in the io_submit(2) syscall or whether there's an issue in QEMU itself that causes the softlockup (for example, aio_poll() with the global mutex held). Stefan --Mit9XoPEfICDqq/V Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl9fb8kACgkQnKSrs4Gr c8gdlgf+K3yZ69f783TTQuSp94r9d/2lOo1Ve02Y66+76qmQ4PwoP+OQAs4CHu/i bIrGFpPlcow+Y9sINabj8Lqpuocmf+UCeWXn3b+6wCujMzYL19giwUu/CM+yvV3l lXpbrq8LPxKhuHuwQjsOniz+RkPjEVabmSLRnPEsmooCru3MVXrCuVYla2szIgSF +onRTRwm7yG6pCFhC34wtJAtMdaS7eAqWSZ5q/+wAsa1Qw7hfgEh1uO7cEt82OqU Kk2JE2aGlksey4vqcFtf1SrQqHdYPbtBNktJK5TD/XqMCVcY3GnhhyyoApSqB5y/ DpfwzrRh4ieF1wg3xNivOCLsV1YafA== =4huk -----END PGP SIGNATURE----- --Mit9XoPEfICDqq/V--