From nobody Thu May 2 23:52:57 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1543486847995862.4032675505288; Thu, 29 Nov 2018 02:20:47 -0800 (PST) Received: from localhost ([::1]:53235 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gSJR8-0000uU-Mx for importer@patchew.org; Thu, 29 Nov 2018 05:20:46 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47885) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gSJOu-0007jg-Iq for qemu-devel@nongnu.org; Thu, 29 Nov 2018 05:18:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gSJOo-00059e-Te for qemu-devel@nongnu.org; Thu, 29 Nov 2018 05:18:28 -0500 Received: from relay.sw.ru ([185.231.240.75]:35106) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gSJOf-00055F-2A; Thu, 29 Nov 2018 05:18:13 -0500 Received: from [10.28.8.145] (helo=kvm.sw.ru) by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gSJOZ-0006vI-V1; Thu, 29 Nov 2018 13:18:08 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-block@nongnu.org, qemu-devel@nongnu.org Date: Thu, 29 Nov 2018 13:18:00 +0300 Message-Id: <20181129101801.6421-2-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20181129101801.6421-1-vsementsov@virtuozzo.com> References: <20181129101801.6421-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v2 1/2] mirror: fix dead-lock X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, jcody@redhat.com, qemu-stable@nongnu.org, mreitz@redhat.com, dplotnikov@virtuozzo.com, den@openvz.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Let start from the beginning: Commit b9e413dd375 (in 2.9) "block: explicitly acquire aiocontext in aio callbacks that need it" added pairs of aio_context_acquire/release to mirror_write_complete and mirror_read_complete, when they were aio callbacks for blk_aio_* calls. Then, commit 2e1990b26e5 (in 3.0) "block/mirror: Convert to coroutines" dropped these blk_aio_* calls, than mirror_write_complete and mirror_read_complete are not callbacks more, and don't need additional aiocontext acquiring. Furthermore, mirror_read_complete calls blk_co_pwritev inside these pair of aio_context_acquire/release, which leads to the following dead-lock with mirror: (gdb) info thr Id Target Id Frame 3 Thread (LWP 145412) "qemu-system-x86" syscall () 2 Thread (LWP 145416) "qemu-system-x86" __lll_lock_wait () * 1 Thread (LWP 145411) "qemu-system-x86" __lll_lock_wait () (gdb) bt #0 __lll_lock_wait () #1 _L_lock_812 () #2 __GI___pthread_mutex_lock #3 qemu_mutex_lock_impl (mutex=3D0x561032dce420 , file=3D0x5610327d8654 "util/main-loop.c", line=3D236) at util/qemu-thread-posix.c:66 #4 qemu_mutex_lock_iothread_impl #5 os_host_main_loop_wait (timeout=3D480116000) at util/main-loop.c:236 #6 main_loop_wait (nonblocking=3D0) at util/main-loop.c:497 #7 main_loop () at vl.c:1892 #8 main Printing contents of qemu_global_mutex, I see that "__owner =3D 145416", so, thr1 is main loop, and now it wants BQL, which is owned by thr2. (gdb) thr 2 (gdb) bt #0 __lll_lock_wait () #1 _L_lock_870 () #2 __GI___pthread_mutex_lock #3 qemu_mutex_lock_impl (mutex=3D0x561034d25dc0, ... #4 aio_context_acquire (ctx=3D0x561034d25d60) #5 dma_blk_cb #6 dma_blk_io #7 dma_blk_read #8 ide_dma_cb #9 bmdma_cmd_writeb #10 bmdma_write #11 memory_region_write_accessor #12 access_with_adjusted_size #15 flatview_write #16 address_space_write #17 address_space_rw #18 kvm_handle_io #19 kvm_cpu_exec #20 qemu_kvm_cpu_thread_fn #21 qemu_thread_start #22 start_thread #23 clone () Printing mutex in fr 2, I see "__owner =3D 145411", so thr2 wants aio context mutex, which is owned by thr1. Classic dead-lock. Then, let's check that aio context is hold by mirror coroutine: just print coroutine stack of first tracked request in mirror job target: (gdb) [...] (gdb) qemu coroutine 0x561035dd0860 #0 qemu_coroutine_switch #1 qemu_coroutine_yield #2 qemu_co_mutex_lock_slowpath #3 qemu_co_mutex_lock #4 qcow2_co_pwritev #5 bdrv_driver_pwritev #6 bdrv_aligned_pwritev #7 bdrv_co_pwritev #8 blk_co_pwritev #9 mirror_read_complete () at block/mirror.c:232 #10 mirror_co_read () at block/mirror.c:370 #11 coroutine_trampoline #12 __start_context Yes it is mirror_read_complete calling blk_co_pwritev after acquiring aio context. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Max Reitz --- block/mirror.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/block/mirror.c b/block/mirror.c index 56d9ef7474..8f52c6215d 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -199,7 +199,6 @@ static void coroutine_fn mirror_write_complete(MirrorOp= *op, int ret) { MirrorBlockJob *s =3D op->s; =20 - aio_context_acquire(blk_get_aio_context(s->common.blk)); if (ret < 0) { BlockErrorAction action; =20 @@ -209,15 +208,14 @@ static void coroutine_fn mirror_write_complete(Mirror= Op *op, int ret) s->ret =3D ret; } } + mirror_iteration_done(op, ret); - aio_context_release(blk_get_aio_context(s->common.blk)); } =20 static void coroutine_fn mirror_read_complete(MirrorOp *op, int ret) { MirrorBlockJob *s =3D op->s; =20 - aio_context_acquire(blk_get_aio_context(s->common.blk)); if (ret < 0) { BlockErrorAction action; =20 @@ -228,12 +226,11 @@ static void coroutine_fn mirror_read_complete(MirrorO= p *op, int ret) } =20 mirror_iteration_done(op, ret); - } else { - ret =3D blk_co_pwritev(s->target, op->offset, - op->qiov.size, &op->qiov, 0); - mirror_write_complete(op, ret); + return; } - aio_context_release(blk_get_aio_context(s->common.blk)); + + ret =3D blk_co_pwritev(s->target, op->offset, op->qiov.size, &op->qiov= , 0); + mirror_write_complete(op, ret); } =20 /* Clip bytes relative to offset to not exceed end-of-file */ --=20 2.18.0 From nobody Thu May 2 23:52:57 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1543486941061184.02314897252984; Thu, 29 Nov 2018 02:22:21 -0800 (PST) Received: from localhost ([::1]:53242 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gSJSd-00026J-4C for importer@patchew.org; Thu, 29 Nov 2018 05:22:19 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47847) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gSJOp-0007Pw-Pr for qemu-devel@nongnu.org; Thu, 29 Nov 2018 05:18:24 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gSJOo-00059j-UX for qemu-devel@nongnu.org; Thu, 29 Nov 2018 05:18:23 -0500 Received: from relay.sw.ru ([185.231.240.75]:35112) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gSJOf-00055E-2S; Thu, 29 Nov 2018 05:18:13 -0500 Received: from [10.28.8.145] (helo=kvm.sw.ru) by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gSJOa-0006vI-7U; Thu, 29 Nov 2018 13:18:08 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-block@nongnu.org, qemu-devel@nongnu.org Date: Thu, 29 Nov 2018 13:18:01 +0300 Message-Id: <20181129101801.6421-3-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20181129101801.6421-1-vsementsov@virtuozzo.com> References: <20181129101801.6421-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v2 2/2] iotests: simple mirror test with kvm on 1G image X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, jcody@redhat.com, qemu-stable@nongnu.org, mreitz@redhat.com, dplotnikov@virtuozzo.com, den@openvz.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" This test is broken without previous commit fixing dead-lock in mirror. Signed-off-by: Vladimir Sementsov-Ogievskiy --- tests/qemu-iotests/235 | 59 ++++++++++++++++++++++++++++++++++++++ tests/qemu-iotests/235.out | 1 + tests/qemu-iotests/group | 1 + 3 files changed, 61 insertions(+) create mode 100755 tests/qemu-iotests/235 create mode 100644 tests/qemu-iotests/235.out diff --git a/tests/qemu-iotests/235 b/tests/qemu-iotests/235 new file mode 100755 index 0000000000..e5d1ae6593 --- /dev/null +++ b/tests/qemu-iotests/235 @@ -0,0 +1,59 @@ +#!/usr/bin/env python +# +# Simple mirror test +# +# Copyright (c) 2018 Virtuozzo International GmbH. All rights reserved. +# +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 2 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . +# + +import sys +import os +import iotests +from iotests import qemu_img_create, qemu_io, file_path + +sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'scrip= ts')) + +from qemu import QEMUMachine + +# Note: +# This test was added to check that mirror dead-lock was fixed (see previo= us +# commit before this test addition). +# And it didn't reproduce if at least one of the following: +# 1. use small image size +# 2. use raw format (not qcow2) +# 3. drop kvm and use iotests.VM() (maybe, because of qtest) (however, it = still +# reproduces, if just drop kvm, but gdb failed to produce full backtrac= es +# for me) +# 4. add iothread + +size =3D '1G' + +iotests.verify_image_format(supported_fmts=3D['raw', 'qcow2']) + +disk, target =3D file_path('disk', 'target') + +# prepare source image +qemu_img_create('-f', iotests.imgfmt, disk, size) +qemu_io('-f', iotests.imgfmt, '-c', 'write 0 ' + size, disk) + +vm =3D QEMUMachine(iotests.qemu_prog) +vm.add_args('-machine', 'pc,accel=3Dkvm') +vm.add_args('-drive', 'id=3Dsrc,file=3D' + disk) +vm.launch() + +print(vm.qmp('drive-mirror', device=3D'src', target=3Dtarget, sync=3D'full= ')) +vm.event_wait('BLOCK_JOB_READY') + +vm.shutdown() diff --git a/tests/qemu-iotests/235.out b/tests/qemu-iotests/235.out new file mode 100644 index 0000000000..d6ccbad8fa --- /dev/null +++ b/tests/qemu-iotests/235.out @@ -0,0 +1 @@ +{u'return': {}} diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group index 8c56a0ad11..61a6d98ebd 100644 --- a/tests/qemu-iotests/group +++ b/tests/qemu-iotests/group @@ -232,3 +232,4 @@ 232 auto quick 233 auto quick 234 auto quick migration +235 auto quick --=20 2.18.0