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 23E69C46CCD for ; Tue, 19 Dec 2023 12:11:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rFYwY-00052O-Ve; Tue, 19 Dec 2023 07:11:27 -0500 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 1rFYwW-00050Y-JK for qemu-devel@nongnu.org; Tue, 19 Dec 2023 07:11:24 -0500 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 1rFYwU-00079I-FX for qemu-devel@nongnu.org; Tue, 19 Dec 2023 07:11:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1702987880; 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=uFGTvwjTibbXIkFU0K/fvsttgEJQFViTyB28RDyjN+I=; b=c3GzohodoLgz2wQ2sQdCnUbCo72JhQ+QvNfW71pKwnxXyC5ltCx2rl+rW0Rcijpgi/nMCN QpVpHeFYWbAgUYV/0cCgZhxdn3b3WZiXafjEvjH2NBYhTtBoO2s++fW1eDkU0KZ+soroKw NBQScCgxJeHOvCoqIL/FFZ+YiTFKA9w= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-10-ToXj3wYvNs6LWgQVbZTQgw-1; Tue, 19 Dec 2023 07:11:17 -0500 X-MC-Unique: ToXj3wYvNs6LWgQVbZTQgw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id CB07485A58C; Tue, 19 Dec 2023 12:11:16 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.175]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1A9161C060AF; Tue, 19 Dec 2023 12:11:11 +0000 (UTC) Date: Tue, 19 Dec 2023 13:11:10 +0100 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Vladimir Sementsov-Ogievskiy , Cleber Rosa , Xie Changlong , Paul Durrant , Ari Sundholm , Jason Wang , Eric Blake , John Snow , Eduardo Habkost , Wen Congyang , Alberto Garcia , Anthony Perard , "Michael S. Tsirkin" , Stefano Stabellini , qemu-block@nongnu.org, Juan Quintela , Paolo Bonzini , Coiby Xu , Fabiano Rosas , Hanna Reitz , Zhang Chen , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Pavel Dovgalyuk , Peter Xu , Emanuele Giuseppe Esposito , Fam Zheng , Leonardo Bras , David Hildenbrand , Li Zhijian , xen-devel@lists.xenproject.org Subject: Re: [PATCH v2 14/14] block: remove outdated AioContext locking comments Message-ID: References: <20231205182011.1976568-1-stefanha@redhat.com> <20231205182011.1976568-15-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231205182011.1976568-15-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.066, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-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 05.12.2023 um 19:20 hat Stefan Hajnoczi geschrieben: > The AioContext lock no longer exists. > > There is one noteworthy change: > > - * More specifically, these functions use BDRV_POLL_WHILE(bs), which > - * requires the caller to be either in the main thread and hold > - * the BlockdriverState (bs) AioContext lock, or directly in the > - * home thread that runs the bs AioContext. Calling them from > - * another thread in another AioContext would cause deadlocks. > + * More specifically, these functions use BDRV_POLL_WHILE(bs), which requires > + * the caller to be either in the main thread or directly in the home thread > + * that runs the bs AioContext. Calling them from another thread in another > + * AioContext would cause deadlocks. > > I am not sure whether deadlocks are still possible. Maybe they have just > moved to the fine-grained locks that have replaced the AioContext. Since > I am not sure if the deadlocks are gone, I have kept the substance > unchanged and just removed mention of the AioContext. > > Signed-off-by: Stefan Hajnoczi > Reviewed-by: Eric Blake I think the deadlock the comment refers to is that AIO_WAIT_WHILE() sits in a blocking aio_poll() and nobody wakes it up because aio_wait_kick() only wakes up the main thread. This deadlock still exists after removing the AioContext lock, so the comment after your change looks right to me. Reviewed-by: Kevin Wolf