From patchwork Fri Jul 2 16:38:31 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 57684 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [199.232.76.165]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 493C91007D2 for ; Sat, 3 Jul 2010 02:54:25 +1000 (EST) Received: from localhost ([127.0.0.1]:60661 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OUjV8-0006Ea-QT for incoming@patchwork.ozlabs.org; Fri, 02 Jul 2010 12:54:06 -0400 Received: from [140.186.70.92] (port=44311 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OUjH2-0004Zg-0e for qemu-devel@nongnu.org; Fri, 02 Jul 2010 12:39:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OUjH0-0001f1-AU for qemu-devel@nongnu.org; Fri, 02 Jul 2010 12:39:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28214) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OUjH0-0001et-25 for qemu-devel@nongnu.org; Fri, 02 Jul 2010 12:39:30 -0400 Received: from int-mx04.intmail.prod.int.phx2.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.17]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o62GdSZC021987 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 2 Jul 2010 12:39:28 -0400 Received: from localhost.localdomain (vpn2-11-67.ams2.redhat.com [10.36.11.67]) by int-mx04.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o62GcbbU023884; Fri, 2 Jul 2010 12:39:26 -0400 From: Kevin Wolf To: anthony@codemonkey.ws Date: Fri, 2 Jul 2010 18:38:31 +0200 Message-Id: <1278088712-12302-23-git-send-email-kwolf@redhat.com> In-Reply-To: <1278088712-12302-1-git-send-email-kwolf@redhat.com> References: <1278088712-12302-1-git-send-email-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.17 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [Qemu-devel] [PATCH 22/23] block: Fix early failure in multiwrite X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org bdrv_aio_writev may call the callback immediately (and it will commonly do so in error cases). Current code doesn't consider this. For details see the comment added by this patch. Signed-off-by: Kevin Wolf --- block.c | 35 +++++++++++++++++++++++++++++------ 1 files changed, 29 insertions(+), 6 deletions(-) diff --git a/block.c b/block.c index 9176dec..e65971c 100644 --- a/block.c +++ b/block.c @@ -2183,8 +2183,29 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs) // Check for mergable requests num_reqs = multiwrite_merge(bs, reqs, num_reqs, mcb); - // Run the aio requests + /* + * Run the aio requests. As soon as one request can't be submitted + * successfully, fail all requests that are not yet submitted (we must + * return failure for all requests anyway) + * + * num_requests cannot be set to the right value immediately: If + * bdrv_aio_writev fails for some request, num_requests would be too high + * and therefore multiwrite_cb() would never recognize the multiwrite + * request as completed. We also cannot use the loop variable i to set it + * when the first request fails because the callback may already have been + * called for previously submitted requests. Thus, num_requests must be + * incremented for each request that is submitted. + * + * The problem that callbacks may be called early also means that we need + * to take care that num_requests doesn't become 0 before all requests are + * submitted - multiwrite_cb() would consider the multiwrite request + * completed. A dummy request that is "completed" by a manual call to + * multiwrite_cb() takes care of this. + */ + mcb->num_requests = 1; + for (i = 0; i < num_reqs; i++) { + mcb->num_requests++; acb = bdrv_aio_writev(bs, reqs[i].sector, reqs[i].qiov, reqs[i].nb_sectors, multiwrite_cb, mcb); @@ -2192,22 +2213,24 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs) // We can only fail the whole thing if no request has been // submitted yet. Otherwise we'll wait for the submitted AIOs to // complete and report the error in the callback. - if (mcb->num_requests == 0) { - reqs[i].error = -EIO; + if (i == 0) { goto fail; } else { - mcb->num_requests++; multiwrite_cb(mcb, -EIO); break; } - } else { - mcb->num_requests++; } } + /* Complete the dummy request */ + multiwrite_cb(mcb, 0); + return 0; fail: + for (i = 0; i < mcb->num_callbacks; i++) { + reqs[i].error = -EIO; + } qemu_free(mcb); return -1; }