From patchwork Thu Oct 19 13:19:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fiona Ebner X-Patchwork-Id: 13429166 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 0BE8ECDB483 for ; Thu, 19 Oct 2023 13:22:21 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qtSyP-0005wo-Cn; Thu, 19 Oct 2023 09:22:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qtSwQ-0004UM-C1; Thu, 19 Oct 2023 09:20:05 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qtSwO-0004Ge-OD; Thu, 19 Oct 2023 09:19:58 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 40EE4430E8; Thu, 19 Oct 2023 15:19:41 +0200 (CEST) From: Fiona Ebner To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, vsementsov@yandex-team.ru, jsnow@redhat.com, hreitz@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, t.lamprecht@proxmox.com Subject: [PATCH 1/3] blockjob: drop AioContext lock before calling bdrv_graph_wrlock() Date: Thu, 19 Oct 2023 15:19:34 +0200 Message-Id: <20231019131936.414246-2-f.ebner@proxmox.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231019131936.414246-1-f.ebner@proxmox.com> References: <20231019131936.414246-1-f.ebner@proxmox.com> MIME-Version: 1.0 Received-SPF: pass client-ip=94.136.29.106; envelope-from=f.ebner@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org Same rationale as in 31b2ddfea3 ("graph-lock: Unlock the AioContext while polling"). Otherwise, a deadlock can happen. The alternative would be to pass a BlockDriverState along to bdrv_graph_wrlock(), but there is no BlockDriverState readily available and it's also better conceptually, because the lock is held for the job. The function is always called with the job's AioContext lock held, via one of the .abort, .clean, .free or .prepare job driver functions. Thus, it's safe to drop it. While mirror_exit_common() does hold a second AioContext lock while calling block_job_remove_all_bdrv(), that is for the main thread's AioContext and does not need to be dropped (bdrv_graph_wrlock(bs) also skips dropping the lock if bdrv_get_aio_context(bs) == qemu_get_aio_context()). Suggested-by: Paolo Bonzini Signed-off-by: Fiona Ebner --- blockjob.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/blockjob.c b/blockjob.c index 807f992b59..953dc1b6dc 100644 --- a/blockjob.c +++ b/blockjob.c @@ -198,7 +198,9 @@ void block_job_remove_all_bdrv(BlockJob *job) * one to make sure that such a concurrent access does not attempt * to process an already freed BdrvChild. */ + aio_context_release(job->job.aio_context); bdrv_graph_wrlock(NULL); + aio_context_acquire(job->job.aio_context); while (job->nodes) { GSList *l = job->nodes; BdrvChild *c = l->data;