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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 526F6C433DB for ; Tue, 9 Mar 2021 15:47:36 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id E81CB64FB8 for ; Tue, 9 Mar 2021 15:47:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E81CB64FB8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36808 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJea6-0005so-Ph for qemu-devel@archiver.kernel.org; Tue, 09 Mar 2021 10:47:34 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56270) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJe9i-0006yw-2u for qemu-devel@nongnu.org; Tue, 09 Mar 2021 10:20:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:22471) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lJe9d-000408-B0 for qemu-devel@nongnu.org; Tue, 09 Mar 2021 10:20:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615303212; 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=mHQ7b9fO6uWr3z0rx2qRCWijwG5x//UW/ZwH6oYegDs=; b=VpRI3G8H01O6OPlghNKPbD1MCseg+KMtDSnGsdZMgeqBT/jKmfKbi0w736GF5i1lEhOZsw yniSAnMYO53YX/8mFFmw+eqZDBSV0CTA7fDS0xi8bkOLvGJ9HLb4derjUvIo6pwIhS2R6v ae4Cysrjh5BOH+TFEnWVKUY2nsaIPLU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-387-PsCIBpFRMtil77wQa8Z9fA-1; Tue, 09 Mar 2021 10:20:09 -0500 X-MC-Unique: PsCIBpFRMtil77wQa8Z9fA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 22858804332; Tue, 9 Mar 2021 15:20:08 +0000 (UTC) Received: from localhost (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTP id EBA3410023B2; Tue, 9 Mar 2021 15:20:01 +0000 (UTC) Date: Tue, 9 Mar 2021 15:20:00 +0000 From: Stefan Hajnoczi To: Greg Kurz Subject: Re: [PATCH 4/4] virtiofsd: Release vu_dispatch_lock when stopping queue Message-ID: References: <20210308123141.26444-1-groug@kaod.org> <20210308123141.26444-5-groug@kaod.org> MIME-Version: 1.0 In-Reply-To: <20210308123141.26444-5-groug@kaod.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="TcVfrnILXvUfMZ2+" Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Michael S. Tsirkin" , qemu-devel@nongnu.org, Vivek Goyal , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --TcVfrnILXvUfMZ2+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Mar 08, 2021 at 01:31:41PM +0100, Greg Kurz wrote: > QEMU can stop a virtqueue by sending a VHOST_USER_GET_VRING_BASE request > to virtiofsd. As with all other vhost-user protocol messages, the thread > that runs the main event loop in virtiofsd takes the vu_dispatch lock in > write mode. This ensures that no other thread can access virtqueues or > memory tables at the same time. >=20 > In the case of VHOST_USER_GET_VRING_BASE, the main thread basically > notifies the queue thread that it should terminate and waits for its > termination: >=20 > main() > virtio_loop() > vu_dispatch_wrlock() > vu_dispatch() > vu_process_message() > vu_get_vring_base_exec() > fv_queue_cleanup_thread() > pthread_join() >=20 > Unfortunately, the queue thread ends up calling virtio_send_msg() > at some point, which itself needs to grab the lock: >=20 > fv_queue_thread() > g_list_foreach() > fv_queue_worker() > fuse_session_process_buf_int() > do_release() > lo_release() > fuse_reply_err() > send_reply() > send_reply_iov() > fuse_send_reply_iov_nofree() > fuse_send_msg() > virtio_send_msg() > vu_dispatch_rdlock() <-- Deadlock ! >=20 > Simply have the main thread to release the lock before going to > sleep and take it back afterwards. A very similar patch was already > sent by Vivek Goyal sometime back: >=20 > https://listman.redhat.com/archives/virtio-fs/2021-January/msg00073.html >=20 > The only difference here is that this done in fv_queue_set_started() > because fv_queue_cleanup_thread() can also be called from virtio_loop() > without the lock being held. >=20 > Signed-off-by: Greg Kurz > --- > tools/virtiofsd/fuse_virtio.c | 6 ++++++ > 1 file changed, 6 insertions(+) Reviewed-by: Stefan Hajnoczi --TcVfrnILXvUfMZ2+ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmBHkiAACgkQnKSrs4Gr c8hKoQf/dSIEA6oml+2/FLPeU13BCp2n/U9wmtf/CmLC8qPFCFETttZer9heoq/v AALuURQzzOJdBCo0R1f//maCfOsDob3hT53ojz7lUaPj4/uRpaiHOjokHSzSvcUq hOq1io7dANA/8VnF5z9xdUt97tEurn25jB1NLw0zBBOBxvEq6kYYrLTfT0ojaqv4 otgsnCId57uO8rWbV5kRDt0mi+vXg/A3EqYvzAw0yokUu1g80+JOC8X5azeB7LY8 yf6d5BQjIqpC6gyusmAfVwfcdHl0KfTsPCTIRPj8xmZ6mmJxiZQFiBwPswb5a+U9 mNxtVa7jNXb+JudW81QBhrEXJAGopg== =XK0P -----END PGP SIGNATURE----- --TcVfrnILXvUfMZ2+--