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 D82ABC7EE30 for ; Tue, 1 Jul 2025 17:19:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uWebL-0007cq-3s; Tue, 01 Jul 2025 13:16:59 -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 1uWebG-000778-TF for qemu-devel@nongnu.org; Tue, 01 Jul 2025 13:16:55 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uWebA-0007GU-GB for qemu-devel@nongnu.org; Tue, 01 Jul 2025 13:16:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1751390205; 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=ZAeVpmcYgM0Ip8hYt5ch/mi/SNEpI48cRrp1tOmMJ14=; b=DEJs2Aw6vTOjfTtAlTUfYC3fpnO803WiIYMTbOx48oNKemwzfeP2qD7J808ydV4k7YzFTx Mi+ttU856IFslCOVent2YYlm3tU6acKmlRWTEK4n4SooSb39M07QpsY0iJmUsnaf/RCe9q Hg09cbXfkO8TbRKVfux09s50Jvtuniw= Received: from mx-prod-mc-02.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-668-nm6EoA53Nf-auvEZgTsdLQ-1; Tue, 01 Jul 2025 13:16:39 -0400 X-MC-Unique: nm6EoA53Nf-auvEZgTsdLQ-1 X-Mimecast-MFC-AGG-ID: nm6EoA53Nf-auvEZgTsdLQ_1751390196 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id F2F6B1955F38; Tue, 1 Jul 2025 17:16:34 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.118]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7241E180045B; Tue, 1 Jul 2025 17:16:29 +0000 (UTC) Date: Tue, 1 Jul 2025 19:16:26 +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 v4 00/48] block: do not drain while holding the graph lock Message-ID: References: <20250530151125.955508-1-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250530151125.955508-1-f.ebner@proxmox.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 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 30.05.2025 um 17:10 hat Fiona Ebner geschrieben: > This series is an attempt to fix a deadlock issue reported by Andrey > here [3]. > > bdrv_drained_begin() polls and is not allowed to be called with the > block graph lock held. Mark the function as GRAPH_UNLOCKED. > > This alone does not catch the issue reported by Andrey, because there > is a bdrv_graph_rdunlock_main_loop() before bdrv_drained_begin() in > the function bdrv_change_aio_context(). That unlock is of course > ineffective if the exclusive lock is held, but it prevents TSA from > finding the issue. > > Thus the bdrv_drained_begin() call from inside > bdrv_change_aio_context() needs to be moved up the call stack before > acquiring the locks. This is the bulk of the series. > > Granular draining is not trivially possible, because many of the > affected functions can recursively call themselves. > > In place where bdrv_drained_begin() calls were removed, assertions > are added, checking the quiesced_counter to ensure that the nodes > already got drained further up in the call stack. I finished review for this series. I had some minor comments on patches 24, 27 and 41. Once we agree what to do there, I can probably just make any changes myself while applying. Kevin