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 84968C54E90 for ; Thu, 22 May 2025 12:38:03 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uI5AQ-0006oc-LN; Thu, 22 May 2025 08:37:02 -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 1uI59r-0006id-S6 for qemu-devel@nongnu.org; Thu, 22 May 2025 08:36:25 -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 1uI59o-0001JC-Lz for qemu-devel@nongnu.org; Thu, 22 May 2025 08:36:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747917377; 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=u5EAsjv9wrL99HIoZp0w2tcHiQs210DoZUmuPnVbrbw=; b=hj8LixGmAGnZWd2Iq9A2DDiCTWa3kG00YcIsibbzxLfgfkART8xTV2WgxRSfEszXm3WFtg CX8b9EygU+3cMoQXCn+fXmGGzXcyvI8stBzZvRK9pdRDq8e5CGH2k7P70oANseu2ygNzbw ePJUliDEmFHbetDP8LDrsVwHNiH4UfM= 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-684-JFf5yhkbNyKrJlwoDfq1Kg-1; Thu, 22 May 2025 08:36:14 -0400 X-MC-Unique: JFf5yhkbNyKrJlwoDfq1Kg-1 X-Mimecast-MFC-AGG-ID: JFf5yhkbNyKrJlwoDfq1Kg_1747917372 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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9B6A11955DB5; Thu, 22 May 2025 12:36:10 +0000 (UTC) Received: from redhat.com (unknown [10.45.226.76]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9A6B0180045B; Thu, 22 May 2025 12:36:04 +0000 (UTC) Date: Thu, 22 May 2025 14:36:01 +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 v2 09/24] block: move drain outside of bdrv_try_change_aio_context() Message-ID: References: <20250520103012.424311-1-f.ebner@proxmox.com> <20250520103012.424311-10-f.ebner@proxmox.com> <67436842-4c8a-4536-ad6f-36952160770e@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <67436842-4c8a-4536-ad6f-36952160770e@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: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.275, 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=unavailable 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 22.05.2025 um 11:56 hat Fiona Ebner geschrieben: > Am 21.05.25 um 18:36 schrieb Kevin Wolf: > > Am 20.05.2025 um 12:29 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". > >> > >> Convert the function to a _locked() version that has to be called with > >> the graph lock held and add a convenience wrapper that has to be > >> called with the graph unlocked, which drains and takes the lock > >> itself. Since bdrv_try_change_aio_context() is global state code, the > >> wrapper is too. > >> > >> Callers are adapted to use the appropriate variant. In the > >> test_set_aio_context() unit test, prior drains can be removed, because > >> draining already happens inside the new wrapper. > > > > I'm not sure what's the difference between qmp_x_blockdev_set_iothread() > > which is converted to _locked() and e.g. qmp_blockdev_mirror(). > > For deciding on the variant, I only looked at whether the caller holds > the graph lock or not. Oh, I see. I was thinking much too complicated once again. Maybe just add "the appropriate variant, depending on whether the caller already holds the lock"? > > The reason I could see in qmp_x_blockdev_set_iothread() is that (as we > > discussed in the RFC version of this series) draining can change the > > graph and that could in theory invalidate bs. But the same is true for > > other functions in blockdev.c. > > Right, my patches are not enough to address that kind of problem. > > > If it's just that qmp_x_blockdev_set_iothread() was easy to fix and the > > others are more complex, that's fine with me, but maybe worth mentioning > > in the commit message. > > Yes, I can mention something in the commit message, maybe: > > Functions like qmp_blockdev_mirror() query the nodes to act on before > draining and locking. In theory, draining could invalidate those nodes. > This kind of issue is not addressed by these commits. Doesn't hurt, but it's also not really needed. Kevin