From patchwork Tue Feb 16 17:56:25 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Bonzini X-Patchwork-Id: 8330241 Return-Path: X-Original-To: patchwork-qemu-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id C2A1CC02AA for ; Tue, 16 Feb 2016 17:59:00 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2603020268 for ; Tue, 16 Feb 2016 17:59:00 +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 5BCD220266 for ; Tue, 16 Feb 2016 17:58:59 +0000 (UTC) Received: from localhost ([::1]:48942 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVjtq-0007sl-Qw for patchwork-qemu-devel@patchwork.kernel.org; Tue, 16 Feb 2016 12:58:58 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41303) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVjrw-0004aY-BQ for qemu-devel@nongnu.org; Tue, 16 Feb 2016 12:57:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVjrv-0002vd-9w for qemu-devel@nongnu.org; Tue, 16 Feb 2016 12:57:00 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54131) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVjrq-0002uK-JB; Tue, 16 Feb 2016 12:56:54 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id 2A84EC0B66E3; Tue, 16 Feb 2016 17:56:54 +0000 (UTC) Received: from donizetti.redhat.com (ovpn-112-51.ams2.redhat.com [10.36.112.51]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u1GHuSWa022072; Tue, 16 Feb 2016 12:56:52 -0500 From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Tue, 16 Feb 2016 18:56:25 +0100 Message-Id: <1455645388-32401-14-git-send-email-pbonzini@redhat.com> In-Reply-To: <1455645388-32401-1-git-send-email-pbonzini@redhat.com> References: <1455645388-32401-1-git-send-email-pbonzini@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: qemu-block@nongnu.org, stefanha@redhat.com Subject: [Qemu-devel] [PATCH 13/16] block: only call aio_poll from iothread 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 aio_poll is not thread safe; for example bdrv_drain can hang if the last in-flight I/O operation is completed in the I/O thread after the main thread has checked bs->in_flight. The bug remains latent as long as all of it is called within aio_context_acquire/aio_context_release, but this will change soon. To fix this, if bdrv_drain is called from outside the I/O thread handle it internally in the BDS, without involving AioContext and aio_poll. Signed-off-by: Paolo Bonzini --- block.c | 2 ++ block/io.c | 21 ++++++++++++++++++--- include/block/block_int.h | 5 ++++- 3 files changed, 24 insertions(+), 4 deletions(-) diff --git a/block.c b/block.c index fb02d7f..601a73f 100644 --- a/block.c +++ b/block.c @@ -267,6 +267,7 @@ BlockDriverState *bdrv_new(void) qemu_co_queue_init(&bs->throttled_reqs[1]); bs->refcnt = 1; bs->aio_context = qemu_get_aio_context(); + qemu_event_init(&bs->in_flight_event, true); QTAILQ_INSERT_TAIL(&all_bdrv_states, bs, bs_list); @@ -2395,6 +2396,7 @@ static void bdrv_delete(BlockDriverState *bs) bdrv_make_anon(bs); QTAILQ_REMOVE(&all_bdrv_states, bs, bs_list); + qemu_event_destroy(&bs->in_flight_event); g_free(bs); } diff --git a/block/io.c b/block/io.c index 04b52c8..ea0546f 100644 --- a/block/io.c +++ b/block/io.c @@ -251,11 +251,24 @@ static void bdrv_drain_recurse(BlockDriverState *bs) static bool bdrv_drain_io_recurse(BlockDriverState *bs) { - BdrvChild *child; + AioContext *ctx = bdrv_get_aio_context(bs); bool waited = false; + BdrvChild *child; while (atomic_read(&bs->in_flight) > 0) { - aio_poll(bdrv_get_aio_context(bs), true); + if (aio_context_in_iothread(ctx)) { + /* This case should not occur at all, except for the + * main thread. + */ + aio_poll(bdrv_get_aio_context(bs), true); + } else { + qemu_event_reset(&bs->in_flight_event); + if (atomic_read(&bs->in_flight) > 0) { + aio_context_release(bdrv_get_aio_context(bs)); + qemu_event_wait(&bs->in_flight_event); + aio_context_acquire(bdrv_get_aio_context(bs)); + } + } waited = true; } @@ -465,7 +478,9 @@ void bdrv_inc_in_flight(BlockDriverState *bs) void bdrv_dec_in_flight(BlockDriverState *bs) { - atomic_dec(&bs->in_flight); + if (atomic_fetch_dec(&bs->in_flight) == 1) { + qemu_event_set(&bs->in_flight_event); + } } static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) diff --git a/include/block/block_int.h b/include/block/block_int.h index 89c38c0..9c96d5d 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -404,9 +404,12 @@ struct BlockDriverState { /* Callback before write request is processed */ NotifierWithReturnList before_write_notifiers; - /* number of in-flight requests; overall and serialising */ + /* number of in-flight requests; overall and serialising. + * in_flight_event is set when in_flight becomes 0. + */ unsigned int in_flight; unsigned int serialising_in_flight; + QemuEvent in_flight_event; /* I/O throttling. * throttle_state tells us if this BDS has I/O limits configured.