From patchwork Fri Apr 1 13:57:38 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fam Zheng X-Patchwork-Id: 8724821 Return-Path: X-Original-To: patchwork-qemu-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 10D8C9F38C for ; Fri, 1 Apr 2016 13:58:05 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5804E2034E for ; Fri, 1 Apr 2016 13:58:04 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id ABA9920392 for ; Fri, 1 Apr 2016 13:57:59 +0000 (UTC) Received: from localhost ([::1]:44548 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1alzaI-0002oB-Qu for patchwork-qemu-devel@patchwork.kernel.org; Fri, 01 Apr 2016 09:57:58 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38617) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1alzaA-0002n0-UQ for qemu-devel@nongnu.org; Fri, 01 Apr 2016 09:57:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1alza9-0002pw-M3 for qemu-devel@nongnu.org; Fri, 01 Apr 2016 09:57:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37480) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1alza3-0002oj-Vt; Fri, 01 Apr 2016 09:57:44 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6FED38051B; Fri, 1 Apr 2016 13:57:43 +0000 (UTC) Received: from lemon.redhat.com (vpn1-7-110.pek2.redhat.com [10.72.7.110]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u31DvdAi028660; Fri, 1 Apr 2016 09:57:40 -0400 From: Fam Zheng To: qemu-devel@nongnu.org Date: Fri, 1 Apr 2016 21:57:38 +0800 Message-Id: <1459519058-29864-1-git-send-email-famz@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Cc: Kevin Wolf , lvivier@redhat.com, qemu-block@nongnu.org, Stefan Hajnoczi , pbonzini@redhat.com Subject: [Qemu-devel] [PATCH v2] block: Fix bdrv_drain in coroutine X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Using the nested aio_poll() in coroutine is a bad idea. This patch replaces the aio_poll loop in bdrv_drain with a BH, if called in coroutine. For example, the bdrv_drain() in mirror.c can hang when a guest issued request is pending on it in qemu_co_mutex_lock(). Mirror coroutine in this case has just finished a request, and the block job is about to complete. It calls bdrv_drain() which waits for the other coroutine to complete. The other coroutine is a scsi-disk request. The deadlock happens when the latter is in turn pending on the former to yield/terminate, in qemu_co_mutex_lock(). The state flow is as below (assuming a qcow2 image): mirror coroutine scsi-disk coroutine ------------------------------------------------------------- do last write qcow2:qemu_co_mutex_lock() ... scsi disk read tracked request begin qcow2:qemu_co_mutex_lock.enter qcow2:qemu_co_mutex_unlock() bdrv_drain while (has tracked request) aio_poll() In the scsi-disk coroutine, the qemu_co_mutex_lock() will never return because the mirror coroutine is blocked in the aio_poll(blocking=true). With this patch, the added qemu_coroutine_yield() allows the scsi-disk coroutine to make progress as expected: mirror coroutine scsi-disk coroutine ------------------------------------------------------------- do last write qcow2:qemu_co_mutex_lock() ... scsi disk read tracked request begin qcow2:qemu_co_mutex_lock.enter qcow2:qemu_co_mutex_unlock() bdrv_drain.enter > schedule BH > qemu_coroutine_yield() > qcow2:qemu_co_mutex_lock.return > ... tracked request end ... (resumed from BH callback) bdrv_drain.return ... Reported-by: Laurent Vivier Suggested-by: Paolo Bonzini Signed-off-by: Fam Zheng Tested-by: Laurent Vivier --- v2: Call qemu_bh_delete() in BH callback. [Paolo] Change the loop to an assertion. [Paolo] Elaborate a bit about the fix in commit log. [Paolo] --- block/io.c | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/block/io.c b/block/io.c index c4869b9..ddcfb4c 100644 --- a/block/io.c +++ b/block/io.c @@ -253,6 +253,43 @@ static void bdrv_drain_recurse(BlockDriverState *bs) } } +typedef struct { + Coroutine *co; + BlockDriverState *bs; + QEMUBH *bh; + bool done; +} BdrvCoDrainData; + +static void bdrv_co_drain_bh_cb(void *opaque) +{ + BdrvCoDrainData *data = opaque; + Coroutine *co = data->co; + + qemu_bh_delete(data->bh); + bdrv_drain(data->bs); + data->done = true; + qemu_coroutine_enter(co, NULL); +} + +static void coroutine_fn bdrv_co_drain(BlockDriverState *bs) +{ + BdrvCoDrainData data; + + assert(qemu_in_coroutine()); + data = (BdrvCoDrainData) { + .co = qemu_coroutine_self(), + .bs = bs, + .done = false, + .bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_drain_bh_cb, &data), + }; + qemu_bh_schedule(data.bh); + + qemu_coroutine_yield(); + /* If we are resumed from some other event (such as an aio completion or a + * timer callback), it is a bug in the caller that should be fixed. */ + assert(data.done); +} + /* * Wait for pending requests to complete on a single BlockDriverState subtree, * and suspend block driver's internal I/O until next request arrives. @@ -269,6 +306,10 @@ void bdrv_drain(BlockDriverState *bs) bool busy = true; bdrv_drain_recurse(bs); + if (qemu_in_coroutine()) { + bdrv_co_drain(bs); + return; + } while (busy) { /* Keep iterating */ bdrv_flush_io_queue(bs);