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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 4FD43C77B75 for ; Wed, 3 May 2023 13:06:57 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1puCBT-00058G-Ce; Wed, 03 May 2023 09:06:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1puCBL-000569-WF for qemu-devel@nongnu.org; Wed, 03 May 2023 09:06:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1puCBH-0002eH-Te for qemu-devel@nongnu.org; Wed, 03 May 2023 09:06:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683119163; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Phu2rUngwbJv3O5WPwObndw41FS7BwEFsVdpGZ12G2o=; b=MjA20ljRzl3jfPkuzyrEiCNfJLcmHX/6jllIzT490eNt2wn9EfbF9ct9YQSFlt2X0MyVTZ 9a6mweYEbJ5dp/PimhVeyFCFWBOJ6//VGgHlnnyafyNtWDQLk696kSaLrDqeBGrs2P1Tp1 wkZfWXvflCgv1uuFEiEYnGsr30sofGs= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-21-PTV4Sh6-PaqKGLOW2cNEKg-1; Wed, 03 May 2023 09:05:59 -0400 X-MC-Unique: PTV4Sh6-PaqKGLOW2cNEKg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 92E9A885627; Wed, 3 May 2023 13:05:58 +0000 (UTC) Received: from localhost (unknown [10.39.195.169]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6C56C2026D16; Wed, 3 May 2023 13:05:57 +0000 (UTC) Date: Wed, 3 May 2023 09:05:50 -0400 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-devel@nongnu.org, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Juan Quintela , Julia Suvorova , xen-devel@lists.xenproject.org, eesposit@redhat.com, Richard Henderson , Fam Zheng , "Michael S. Tsirkin" , Coiby Xu , David Woodhouse , Marcel Apfelbaum , Peter Lieven , Paul Durrant , "Richard W.M. Jones" , qemu-block@nongnu.org, Stefano Garzarella , Anthony Perard , Stefan Weil , Xie Yongji , Paolo Bonzini , Aarushi Mehta , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Eduardo Habkost , Stefano Stabellini , Hanna Reitz , Ronnie Sahlberg , Zhengui Li , Daniil Tatianin Subject: Re: [PATCH v4 04/20] virtio-scsi: stop using aio_disable_external() during unplug Message-ID: <20230503130550.GA757667@fedora> References: <20230425172716.1033562-1-stefanha@redhat.com> <20230425172716.1033562-5-stefanha@redhat.com> <20230501150934.GA14869@fedora> <20230502200243.GD535070@fedora> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="SX9dxWjHVceQRg4J" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.161, 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, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --SX9dxWjHVceQRg4J Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, May 03, 2023 at 01:40:49PM +0200, Kevin Wolf wrote: > Am 02.05.2023 um 22:02 hat Stefan Hajnoczi geschrieben: > > On Tue, May 02, 2023 at 03:19:52PM +0200, Kevin Wolf wrote: > > > Am 01.05.2023 um 17:09 hat Stefan Hajnoczi geschrieben: > > > > On Fri, Apr 28, 2023 at 04:22:55PM +0200, Kevin Wolf wrote: > > > > > Am 25.04.2023 um 19:27 hat Stefan Hajnoczi geschrieben: > > > > > > This patch is part of an effort to remove the aio_disable_exter= nal() > > > > > > API because it does not fit in a multi-queue block layer world = where > > > > > > many AioContexts may be submitting requests to the same disk. > > > > > >=20 > > > > > > The SCSI emulation code is already in good shape to stop using > > > > > > aio_disable_external(). It was only used by commit 9c5aad84da1c > > > > > > ("virtio-scsi: fixed virtio_scsi_ctx_check failed when detachin= g scsi > > > > > > disk") to ensure that virtio_scsi_hotunplug() works while the g= uest > > > > > > driver is submitting I/O. > > > > > >=20 > > > > > > Ensure virtio_scsi_hotunplug() is safe as follows: > > > > > >=20 > > > > > > 1. qdev_simple_device_unplug_cb() -> qdev_unrealize() -> > > > > > > device_set_realized() calls qatomic_set(&dev->realized, fals= e) so > > > > > > that future scsi_device_get() calls return NULL because they= exclude > > > > > > SCSIDevices with realized=3Dfalse. > > > > > >=20 > > > > > > That means virtio-scsi will reject new I/O requests to this > > > > > > SCSIDevice with VIRTIO_SCSI_S_BAD_TARGET even while > > > > > > virtio_scsi_hotunplug() is still executing. We are protected= against > > > > > > new requests! > > > > > >=20 > > > > > > 2. Add a call to scsi_device_purge_requests() from scsi_unreali= ze() so > > > > > > that in-flight requests are cancelled synchronously. This en= sures > > > > > > that no in-flight requests remain once qdev_simple_device_un= plug_cb() > > > > > > returns. > > > > > >=20 > > > > > > Thanks to these two conditions we don't need aio_disable_extern= al() > > > > > > anymore. > > > > > >=20 > > > > > > Cc: Zhengui Li > > > > > > Reviewed-by: Paolo Bonzini > > > > > > Reviewed-by: Daniil Tatianin > > > > > > Signed-off-by: Stefan Hajnoczi > > > > >=20 > > > > > qemu-iotests 040 starts failing for me after this patch, with wha= t looks > > > > > like a use-after-free error of some kind. > > > > >=20 > > > > > (gdb) bt > > > > > #0 0x000055b6e3e1f31c in job_type (job=3D0xe3e3e3e3e3e3e3e3) at = =2E./job.c:238 > > > > > #1 0x000055b6e3e1cee5 in is_block_job (job=3D0xe3e3e3e3e3e3e3e3)= at ../blockjob.c:41 > > > > > #2 0x000055b6e3e1ce7d in block_job_next_locked (bjob=3D0x55b6e72= b7570) at ../blockjob.c:54 > > > > > #3 0x000055b6e3df6370 in blockdev_mark_auto_del (blk=3D0x55b6e74= af0a0) at ../blockdev.c:157 > > > > > #4 0x000055b6e393e23b in scsi_qdev_unrealize (qdev=3D0x55b6e7c04= d40) at ../hw/scsi/scsi-bus.c:303 > > > > > #5 0x000055b6e3db0d0e in device_set_realized (obj=3D0x55b6e7c04d= 40, value=3Dfalse, errp=3D0x55b6e497c918 ) at ../hw/core/qdev.= c:599 > > > > > #6 0x000055b6e3dba36e in property_set_bool (obj=3D0x55b6e7c04d40= , v=3D0x55b6e7d7f290, name=3D0x55b6e41bd6d8 "realized", opaque=3D0x55b6e724= 6d20, errp=3D0x55b6e497c918 ) > > > > > at ../qom/object.c:2285 > > > > > #7 0x000055b6e3db7e65 in object_property_set (obj=3D0x55b6e7c04d= 40, name=3D0x55b6e41bd6d8 "realized", v=3D0x55b6e7d7f290, errp=3D0x55b6e497= c918 ) at ../qom/object.c:1420 > > > > > #8 0x000055b6e3dbd84a in object_property_set_qobject (obj=3D0x55= b6e7c04d40, name=3D0x55b6e41bd6d8 "realized", value=3D0x55b6e74c1890, errp= =3D0x55b6e497c918 ) > > > > > at ../qom/qom-qobject.c:28 > > > > > #9 0x000055b6e3db8570 in object_property_set_bool (obj=3D0x55b6e= 7c04d40, name=3D0x55b6e41bd6d8 "realized", value=3Dfalse, errp=3D0x55b6e497= c918 ) at ../qom/object.c:1489 > > > > > #10 0x000055b6e3daf2b5 in qdev_unrealize (dev=3D0x55b6e7c04d40) a= t ../hw/core/qdev.c:306 > > > > > #11 0x000055b6e3db509d in qdev_simple_device_unplug_cb (hotplug_d= ev=3D0x55b6e81c3630, dev=3D0x55b6e7c04d40, errp=3D0x7ffec5519200) at ../hw/= core/qdev-hotplug.c:72 > > > > > #12 0x000055b6e3c520f9 in virtio_scsi_hotunplug (hotplug_dev=3D0x= 55b6e81c3630, dev=3D0x55b6e7c04d40, errp=3D0x7ffec5519200) at ../hw/scsi/vi= rtio-scsi.c:1065 > > > > > #13 0x000055b6e3db4dec in hotplug_handler_unplug (plug_handler=3D= 0x55b6e81c3630, plugged_dev=3D0x55b6e7c04d40, errp=3D0x7ffec5519200) at ../= hw/core/hotplug.c:56 > > > > > #14 0x000055b6e3a28f84 in qdev_unplug (dev=3D0x55b6e7c04d40, errp= =3D0x7ffec55192e0) at ../softmmu/qdev-monitor.c:935 > > > > > #15 0x000055b6e3a290fa in qmp_device_del (id=3D0x55b6e74c1760 "sc= si0", errp=3D0x7ffec55192e0) at ../softmmu/qdev-monitor.c:955 > > > > > #16 0x000055b6e3fb0a5f in qmp_marshal_device_del (args=3D0x7f61cc= 005eb0, ret=3D0x7f61d5a8ae38, errp=3D0x7f61d5a8ae40) at qapi/qapi-commands-= qdev.c:114 > > > > > #17 0x000055b6e3fd52e1 in do_qmp_dispatch_bh (opaque=3D0x7f61d5a8= ae08) at ../qapi/qmp-dispatch.c:128 > > > > > #18 0x000055b6e4007b9e in aio_bh_call (bh=3D0x55b6e7dea730) at ..= /util/async.c:155 > > > > > #19 0x000055b6e4007d2e in aio_bh_poll (ctx=3D0x55b6e72447c0) at .= =2E/util/async.c:184 > > > > > #20 0x000055b6e3fe3b45 in aio_dispatch (ctx=3D0x55b6e72447c0) at = =2E./util/aio-posix.c:421 > > > > > #21 0x000055b6e4009544 in aio_ctx_dispatch (source=3D0x55b6e72447= c0, callback=3D0x0, user_data=3D0x0) at ../util/async.c:326 > > > > > #22 0x00007f61ddc14c7f in g_main_dispatch (context=3D0x55b6e7244b= 20) at ../glib/gmain.c:3454 > > > > > #23 g_main_context_dispatch (context=3D0x55b6e7244b20) at ../glib= /gmain.c:4172 > > > > > #24 0x000055b6e400a7e8 in glib_pollfds_poll () at ../util/main-lo= op.c:290 > > > > > #25 0x000055b6e400a0c2 in os_host_main_loop_wait (timeout=3D0) at= ../util/main-loop.c:313 > > > > > #26 0x000055b6e4009fa2 in main_loop_wait (nonblocking=3D0) at ../= util/main-loop.c:592 > > > > > #27 0x000055b6e3a3047b in qemu_main_loop () at ../softmmu/runstat= e.c:731 > > > > > #28 0x000055b6e3dab27d in qemu_default_main () at ../softmmu/main= =2Ec:37 > > > > > #29 0x000055b6e3dab2b8 in main (argc=3D24, argv=3D0x7ffec55196a8)= at ../softmmu/main.c:48 > > > > > (gdb) p jobs > > > > > $4 =3D {lh_first =3D 0x0} > > > >=20 > > > > I wasn't able to reproduce this with gcc 13.1.1 or clang 16.0.1: > > > >=20 > > > > $ tests/qemu-iotests/check -qcow2 040 > > > >=20 > > > > Any suggestions on how to reproduce the issue? > > >=20 > > > It happens consistently for me with the same command line, both with = gcc > > > and clang. > > >=20 > > > gcc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4) > > > clang version 15.0.7 (Fedora 15.0.7-2.fc37) > > >=20 > > > Maybe there is a semantic merge conflict? I have applied the series on > > > top of master (05d50ba2d4) and my block branch (88f81f7bc8). > >=20 > > I can't find 88f81f7bc8 but rebased on repo.or.cz/qemu/kevin.git block > > (4514dac7f2e9) and the test passes here. > >=20 > > I rebased on qemu.git/master (05d50ba2d4) and it also passes. > >=20 > > Please let me know if the following tree (a0ff680a72f6) works on your > > machine: > > https://gitlab.com/stefanha/qemu/-/tree/remove-aio_disable_external >=20 > Fails in the same way. >=20 > So I tried to debug this myself now. The problem is that iterating the > jobs in blockdev_mark_auto_del() is incorrect: job_cancel_locked() > frees the job and then block_job_next_locked() is a use after free. >=20 > It also drops job_mutex temporarily and polls, so even switching to a > *_FOREACH_SAFE style loop won't fix this. I guess we have to restart > the whole search from the start after a job_cancel_locked() because the > list might look very different after the call. >=20 > Now, of course, how this is related to your patch and why it doesn't > trigger before it, is still less than clear. What I found out is that > adding the scsi_device_purge_requests() is enough to crash it. Maybe > it's related to the blk_drain() inside of it. That the job finishes > earlier during the unplug now or something like that. >=20 > Anyway, changing blockdev_mark_auto_del() fixes it. I'll send a patch. Thanks, and sorry for taking your time with debugging it! Stefan --SX9dxWjHVceQRg4J Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmRSXC4ACgkQnKSrs4Gr c8i74Qf6AklkO6aWrRBz6XAZ8dK/EiYL1W+TDr0RyrsU7nCVkvdlyP7AlGvIyjcs YrK8FIjM+cjgHKnMkRqFBMn0xVQMrnSNZ2cLDZaVY4DlgVlmYmmt0RNnQWlftAuc UJkymWg5dZV6hw/TI7ku1+pRnZRx32fxLiMIn+R1tkD8+OX+JMeN7WG3cAhvpPUI m24TcHXZrqNO0kV4qXoM4GJNkDkYLaF1pXQ4MsZpPHcr8Zzhyn+5vlVmo+FEp7iX ozXdMSGcA+fQ3yUGEIUISvZMrc3f8aIfaV29gti8Sj+ekULPGAS9It/2ZJuZTRos Rbou/5fwuiQX6myLLQCGj7HQuwlZ+g== =GY3E -----END PGP SIGNATURE----- --SX9dxWjHVceQRg4J--