From nobody Sat Nov 15 19:39:03 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1748618301374734.2066751358475; Fri, 30 May 2025 08:18:21 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uL1PC-0003Kh-5x; Fri, 30 May 2025 11:12:22 -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 1uL1P7-00036r-Cv; Fri, 30 May 2025 11:12:17 -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 1uL1P5-0002GH-Ps; Fri, 30 May 2025 11:12:17 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id EA2CE44AAB; Fri, 30 May 2025 17:11:43 +0200 (CEST) From: Fiona Ebner To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, kwolf@redhat.com, den@virtuozzo.com, andrey.drobyshev@virtuozzo.com, hreitz@redhat.com, stefanha@redhat.com, eblake@redhat.com, jsnow@redhat.com, vsementsov@yandex-team.ru, xiechanglong.d@gmail.com, wencongyang2@huawei.com, berto@igalia.com, fam@euphon.net, ari@tuxera.com Subject: [PATCH v4 11/48] block: move drain outside of bdrv_set_backing_hd_drained() Date: Fri, 30 May 2025 17:10:48 +0200 Message-Id: <20250530151125.955508-12-f.ebner@proxmox.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250530151125.955508-1-f.ebner@proxmox.com> References: <20250530151125.955508-1-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; 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, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1748618303465116600 Content-Type: text/plain; charset="utf-8" This is part of resolving the deadlock mentioned in commit "block: move draining out of bdrv_change_aio_context() and mark GRAPH_RDLOCK". The function bdrv_set_backing_hd_drained() holds the graph lock, so it is not allowed to drain. It is called by: 1. bdrv_set_backing_hd(), where a drained section is introduced, replacing the previously present bs-specific drains. 2. stream_prepare(), where a drained section is introduced replacing the previously present bs-specific drains. The drain_bs variable in bdrv_set_backing_hd_drained() is now superfluous and thus dropped. Signed-off-by: Fiona Ebner --- Changes in v4: * Drop now superfluous drain_bs variable. * Document requirement that all nodes need to be drained for bdrv_set_backing_hd_drained(). block.c | 16 +++------------- block/stream.c | 6 ++---- 2 files changed, 5 insertions(+), 17 deletions(-) diff --git a/block.c b/block.c index 46eb2fe449..e53a88e1b6 100644 --- a/block.c +++ b/block.c @@ -3562,8 +3562,7 @@ out: * Both @bs and @backing_hd can move to a different AioContext in this * function. * - * If a backing child is already present (i.e. we're detaching a node), th= at - * child node must be drained. + * All block nodes must be drained. */ int bdrv_set_backing_hd_drained(BlockDriverState *bs, BlockDriverState *backing_hd, @@ -3578,7 +3577,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs, assert(bs->backing->bs->quiesce_counter > 0); } =20 - bdrv_drain_all_begin(); ret =3D bdrv_set_file_or_backing_noperm(bs, backing_hd, true, tran, er= rp); if (ret < 0) { goto out; @@ -3587,28 +3585,20 @@ int bdrv_set_backing_hd_drained(BlockDriverState *b= s, ret =3D bdrv_refresh_perms(bs, tran, errp); out: tran_finalize(tran, ret); - bdrv_drain_all_end(); return ret; } =20 int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd, Error **errp) { - BlockDriverState *drain_bs; int ret; GLOBAL_STATE_CODE(); =20 - bdrv_graph_rdlock_main_loop(); - drain_bs =3D bs->backing ? bs->backing->bs : bs; - bdrv_graph_rdunlock_main_loop(); - - bdrv_ref(drain_bs); - bdrv_drained_begin(drain_bs); + bdrv_drain_all_begin(); bdrv_graph_wrlock(); ret =3D bdrv_set_backing_hd_drained(bs, backing_hd, errp); bdrv_graph_wrunlock(); - bdrv_drained_end(drain_bs); - bdrv_unref(drain_bs); + bdrv_drain_all_end(); =20 return ret; } diff --git a/block/stream.c b/block/stream.c index 999d9e56d4..6ba49cffd3 100644 --- a/block/stream.c +++ b/block/stream.c @@ -80,11 +80,10 @@ static int stream_prepare(Job *job) * may end up working with the wrong base node (or it might even have = gone * away by the time we want to use it). */ - bdrv_drained_begin(unfiltered_bs); if (unfiltered_bs_cow) { bdrv_ref(unfiltered_bs_cow); - bdrv_drained_begin(unfiltered_bs_cow); } + bdrv_drain_all_begin(); =20 bdrv_graph_rdlock_main_loop(); base =3D bdrv_filter_or_cow_bs(s->above_base); @@ -123,11 +122,10 @@ static int stream_prepare(Job *job) } =20 out: + bdrv_drain_all_end(); if (unfiltered_bs_cow) { - bdrv_drained_end(unfiltered_bs_cow); bdrv_unref(unfiltered_bs_cow); } - bdrv_drained_end(unfiltered_bs); return ret; } =20 --=20 2.39.5