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 8648FC761A6 for ; Mon, 27 Mar 2023 13:16:11 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pgmgo-0002mx-P3; Mon, 27 Mar 2023 09:15:10 -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 1pgmgm-0002kD-VK for qemu-devel@nongnu.org; Mon, 27 Mar 2023 09:15:09 -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 1pgmgj-0001pO-2s for qemu-devel@nongnu.org; Mon, 27 Mar 2023 09:15:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679922903; 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=Zv4Vcg2eIl2ktnMY8c5mrUNzhhYHtvOW2ohZj7cVldE=; b=SJfcpD3bLEjJw8ISrYvVcgDhjwvt+KZRLh3qTIxwa5nog+blSBI2DTslUB75CIcm2Hvcx6 uxo9MDZa9R4OLjSh2isDv1OlMOek4Rjhb8dOO6YIXk7gBk9KJqGMb/+Myg993mlDikv+w9 vegRuml5Ut6etN1z9P3ih6ST5iZsur0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-617-PmgY0Cs5OO2BamJ5zRiT-w-1; Mon, 27 Mar 2023 09:15:00 -0400 X-MC-Unique: PmgY0Cs5OO2BamJ5zRiT-w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BE1B9858F09; Mon, 27 Mar 2023 13:14:59 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 99FE6C15BA0; Mon, 27 Mar 2023 13:14:58 +0000 (UTC) Date: Mon, 27 Mar 2023 15:14:57 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Fam Zheng , qemu-stable@nongnu.org, Qing Wang , Paolo Bonzini Subject: Re: [PATCH for-8.0 v2] aio-posix: fix race between epoll upgrade and aio_set_fd_handler() Message-ID: References: <20230323144859.1338495-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230323144859.1338495-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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: -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_H2=-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 23.03.2023 um 15:48 hat Stefan Hajnoczi geschrieben: > If another thread calls aio_set_fd_handler() while the IOThread event > loop is upgrading from ppoll(2) to epoll(7) then we might miss new > AioHandlers. The epollfd will not monitor the new AioHandler's fd, > resulting in hangs. > > Take the AioHandler list lock while upgrading to epoll. This prevents > AioHandlers from changing while epoll is being set up. If we cannot lock > because we're in a nested event loop, then don't upgrade to epoll (it > will happen next time we're not in a nested call). > > The downside to taking the lock is that the aio_set_fd_handler() thread > has to wait until the epoll upgrade is finished, which involves many > epoll_ctl(2) system calls. However, this scenario is rare and I couldn't > think of another solution that is still simple. > > Reported-by: Qing Wang > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2090998 > Cc: Paolo Bonzini > Cc: Fam Zheng > Signed-off-by: Stefan Hajnoczi > --- > v2: > - Use qemu_lockcnt_inc_and_unlock() instead of qemu_lockcnt_unlock() [Paolo] Thanks, applied to the block branch. Kevin