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 D9479C19F21 for ; Thu, 4 Aug 2022 19:07:54 +0000 (UTC) Received: from localhost ([::1]:58898 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oJgCH-0007LC-J9 for qemu-devel@archiver.kernel.org; Thu, 04 Aug 2022 15:07:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39298) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJg1s-0004HB-UR for qemu-devel@nongnu.org; Thu, 04 Aug 2022 14:57:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:52003) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJg1q-0007Fi-8q for qemu-devel@nongnu.org; Thu, 04 Aug 2022 14:57:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659639425; 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=oMwE49k6wAEt2QTWRx2yBXc/bHja+0uTUo3+UyjnlKs=; b=Ol+9X3C1flupyubefxj/Hh8kJ7Z87YfUhJ/e3xg0IDKIQIimvxfNH004hIL8C3Yx6AS7F9 IKQAf2fyy3mFBN5PecSBvA+EPo3ihEyPPsJgDBRFbYTm/kBZfJCMKf/0oeDVsokYreDP4y HVeCANqvBwHgZG1Tx8y5bsFzvxe3CGg= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-245-5xgLgTRyOSafDTfXNHHiCQ-1; Thu, 04 Aug 2022 14:57:02 -0400 X-MC-Unique: 5xgLgTRyOSafDTfXNHHiCQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 59A0B3C0E21E; Thu, 4 Aug 2022 18:57:01 +0000 (UTC) Received: from localhost (unknown [10.39.192.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id B51571121314; Thu, 4 Aug 2022 18:57:00 +0000 (UTC) Date: Thu, 4 Aug 2022 14:56:59 -0400 From: Stefan Hajnoczi To: qemu-devel@nongnu.org, "Michael S. Tsirkin" , pbonzini@redhat.com Cc: sgarzare@redhat.com, kwolf@redhat.com, Emanuele Giuseppe Esposito , Fam Zheng , Qing Wang Subject: Re: [PATCH 7.1] virtio-scsi: fix race in virtio_scsi_dataplane_start() Message-ID: References: <20220803162824.948023-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="fxODSeY07Sy3WE1f" Content-Disposition: inline In-Reply-To: <20220803162824.948023-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 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: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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" --fxODSeY07Sy3WE1f Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 03, 2022 at 12:28:24PM -0400, Stefan Hajnoczi wrote: > As soon as virtio_scsi_data_plane_start() attaches host notifiers the > IOThread may start virtqueue processing. There is a race between > IOThread virtqueue processing and virtio_scsi_data_plane_start() because > it only assigns s->dataplane_started after attaching host notifiers. >=20 > When a virtqueue handler function in the IOThread calls > virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and > attempt to start dataplane even though we're already in the IOThread: >=20 > #0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa25= 7c) > #1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56) > #2 0x00007f67b358e833 abort (libc.so.6 + 0x28833) > #3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b) > #4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6) > #5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x6= 7511b) > #6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811) > #7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b583= 6) > #8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f1= 4e) > #9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62) > #10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610) > #11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a) > #12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x64= 6902) > #13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e) > #14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761) > #15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052) > #16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a) >=20 > This patch assigns s->dataplane_started before attaching host notifiers > so that virtqueue handler functions that run in the IOThread before > virtio_scsi_data_plane_start() returns correctly identify that dataplane > does not need to be started. >=20 > Note that s->dataplane_started does not need the AioContext lock because > it is set before attaching host notifiers and cleared after detaching > host notifiers. In other words, the IOThread always sees the value true > and the main loop thread does not modify it while the IOThread is > active. >=20 > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=3D2099541 > Reported-by: Qing Wang Qing Wang has confirmed that this solves the assertion failures. Paolo/Michael: Can this still be merged for QEMU 7.1? Stefan --fxODSeY07Sy3WE1f Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmLsFnsACgkQnKSrs4Gr c8iyoQf8D+UIJ2LA37Cz7RmIuOr+b+1VNX0sypZL+N60UauVMwk5o94cDQa3ER7j /1QmqYKVU4Q+RSNU8jh917P2bOBKaMNS7dqb0ZQz1pz5CxaJSZOb1EUkEeECjmmr R3h6euJn05ncM3tHP516Ubda9q958+BlX9CYkO20D/jWb/eYWbFFBRRNhaZxPV79 gbJaPRUl92D5wV18X5Qm6Z2dY9RsXyWuMaI7qbriTJjbcFT7AJrExDWwDbTUGqPQ c3ThopSbO78U5FB+FXIbf+/4VjFwoS6tajAyfwMyUcYDB6ORu835dGniYT4H7CA/ UJfGrUE69UXYs4lkfDhrAnnY9SOUag== =6G2m -----END PGP SIGNATURE----- --fxODSeY07Sy3WE1f--