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=-15.1 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,USER_AGENT_SANE_1 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 DD39EC433DB for ; Mon, 15 Mar 2021 14:59:11 +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 4F0D260249 for ; Mon, 15 Mar 2021 14:59:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F0D260249 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]:54822 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lLogY-000231-Es for qemu-devel@archiver.kernel.org; Mon, 15 Mar 2021 10:59:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35228) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lLof6-0001BL-ND for qemu-devel@nongnu.org; Mon, 15 Mar 2021 10:57:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:51815) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lLof3-0007Ay-Ve for qemu-devel@nongnu.org; Mon, 15 Mar 2021 10:57:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615820257; 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=XxBN8tSi8xbjQVI1gT0IG2P4x4wS7ksv+7xsFhNflss=; b=DoiyZIMkBbgto42xDXENyukRWGQ6mlasLwuW8V3yJBc3rQSNX2eJXB0L62/XGGngzzSz21 XbEttMi+so1/TLkXetyr8ZEaiJrtXEYU6W9dfYliu37DQxFKyQ0xrLmReblVwZ00MereUI vaa9dkrKDDN0JHPt/sGUkD88P5Ao/OE= 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-213-uvQduHRQOFWmubB1K9Dc9w-1; Mon, 15 Mar 2021 10:57:35 -0400 X-MC-Unique: uvQduHRQOFWmubB1K9Dc9w-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3102119200C1; Mon, 15 Mar 2021 14:57:34 +0000 (UTC) Received: from work-vm (ovpn-114-235.ams2.redhat.com [10.36.114.235]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 670725D9D3; Mon, 15 Mar 2021 14:57:20 +0000 (UTC) Date: Mon, 15 Mar 2021 14:57:17 +0000 From: "Dr. David Alan Gilbert" To: Greg Kurz Subject: Re: [PATCH v2 7/7] virtiofsd: Release vu_dispatch_lock when stopping queue Message-ID: References: <20210312092212.782255-1-groug@kaod.org> <20210312092212.782255-8-groug@kaod.org> MIME-Version: 1.0 In-Reply-To: <20210312092212.782255-8-groug@kaod.org> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@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=-0.25, 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: Daniel P =?iso-8859-1?Q?=2E_Berrang=E9?= , "Michael S. Tsirkin" , qemu-devel@nongnu.org, virtio-fs@redhat.com, Stefan Hajnoczi , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Greg Kurz (groug@kaod.org) 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. > > 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: > > main() > virtio_loop() > vu_dispatch_wrlock() > vu_dispatch() > vu_process_message() > vu_get_vring_base_exec() > fv_queue_cleanup_thread() > pthread_join() > > Unfortunately, the queue thread ends up calling virtio_send_msg() > at some point, which itself needs to grab the lock: > > 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 ! > > 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: > > https://listman.redhat.com/archives/virtio-fs/2021-January/msg00073.html > > 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. > > Signed-off-by: Greg Kurz > Reviewed-by: Vivek Goyal > Reviewed-by: Stefan Hajnoczi I've queued just this 7/7 in the virtiofsd pull I'm just making at the moment. I'll leave the rest to ride the vhost-user train. Dave > --- > tools/virtiofsd/fuse_virtio.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c > index 523ee64fb7ae..3e13997406bf 100644 > --- a/tools/virtiofsd/fuse_virtio.c > +++ b/tools/virtiofsd/fuse_virtio.c > @@ -792,7 +792,13 @@ static void fv_queue_set_started(VuDev *dev, int qidx, bool started) > assert(0); > } > } else { > + /* > + * Temporarily drop write-lock taken in virtio_loop() so that > + * the queue thread doesn't block in virtio_send_msg(). > + */ > + vu_dispatch_unlock(vud); > fv_queue_cleanup_thread(vud, qidx); > + vu_dispatch_wrlock(vud); > } > } > > -- > 2.26.2 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK