From mboxrd@z Thu Jan 1 00:00:00 1970 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 B3641C54F30 for ; Tue, 27 May 2025 15:30:39 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uJwFW-0001gX-AU; Tue, 27 May 2025 11:29:54 -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 1uJwFU-0001g1-8S for qemu-devel@nongnu.org; Tue, 27 May 2025 11:29:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uJwFQ-0001O1-PA for qemu-devel@nongnu.org; Tue, 27 May 2025 11:29:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1748359786; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CCvPT9Qh8N6WBHksbMF8yPY2VPhwxxJPUp9k1VX1H90=; b=a1Wb30k4hSw6S539Y9mdI1YFha+FEfVj6romVy3Uu64J80/qWK66iWC6kIZ+wi5aJWVg54 jPCsC07lAhnOWbZRE7T87Y49J1sUW1aQflIL9edjaqm3yU27YIfmpEES9HGJtfViwAW5zd QYtw4XqSgzOlhJVFv32QSopSEGKXdq8= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-25-XMg1hHCNMzWg-4xzvzttnw-1; Tue, 27 May 2025 11:29:42 -0400 X-MC-Unique: XMg1hHCNMzWg-4xzvzttnw-1 X-Mimecast-MFC-AGG-ID: XMg1hHCNMzWg-4xzvzttnw_1748359781 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0E2AF1954236; Tue, 27 May 2025 15:29:40 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.20]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B4BF430001B0; Tue, 27 May 2025 15:29:34 +0000 (UTC) Date: Tue, 27 May 2025 17:29:31 +0200 From: Kevin Wolf To: Fiona Ebner Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, 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: Re: [PATCH v3 11/24] block: move drain outside of bdrv_set_backing_hd_drained() Message-ID: References: <20250526132140.1641377-1-f.ebner@proxmox.com> <20250526132140.1641377-12-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250526132140.1641377-12-f.ebner@proxmox.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -49 X-Spam_score: -5.0 X-Spam_bar: ----- X-Spam_report: (-5.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.907, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 26.05.2025 um 15:21 hat Fiona Ebner geschrieben: > 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. > > Signed-off-by: Fiona Ebner > --- > > No changes in v3. > > block.c | 6 ++---- > block/stream.c | 6 ++---- > 2 files changed, 4 insertions(+), 8 deletions(-) > > diff --git a/block.c b/block.c > index 64db71e38d..75322789b5 100644 > --- a/block.c > +++ b/block.c > @@ -3569,7 +3569,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs, > assert(bs->backing->bs->quiesce_counter > 0); > } > > - bdrv_drain_all_begin(); > ret = bdrv_set_file_or_backing_noperm(bs, backing_hd, true, tran, errp); > if (ret < 0) { > goto out; > @@ -3578,7 +3577,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs, > ret = bdrv_refresh_perms(bs, tran, errp); > out: > tran_finalize(tran, ret); > - bdrv_drain_all_end(); > return ret; > } Do we need to update the comment for bdrv_set_backing_hd_drained()? * If a backing child is already present (i.e. we're detaching a node), that * child node must be drained. Same as in the previous patch, this is now probably all nodes. > @@ -3594,11 +3592,11 @@ int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd, > bdrv_graph_rdunlock_main_loop(); > > bdrv_ref(drain_bs); > - bdrv_drained_begin(drain_bs); > + bdrv_drain_all_begin(); > bdrv_graph_wrlock(); > ret = bdrv_set_backing_hd_drained(bs, backing_hd, errp); > bdrv_graph_wrunlock(); > - bdrv_drained_end(drain_bs); > + bdrv_drain_all_end(); > bdrv_unref(drain_bs); The only thing we do with drain_bs now is finding it, bdrv_ref() and immediately bdrv_unref(). I don't think it should exist any more after the change to drain_all. Kevin