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 0A81EC77B7A for ; Tue, 30 May 2023 16:40:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q42Im-0001Ru-GM; Tue, 30 May 2023 12:34:28 -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 1q42Hg-0006wX-RP for qemu-devel@nongnu.org; Tue, 30 May 2023 12:33:28 -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 1q42He-0008TB-NB for qemu-devel@nongnu.org; Tue, 30 May 2023 12:33:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685464395; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dWYtO63hzJuGikLX2mgXYxihjvj+ywyd+OvX6djxaX8=; b=Q+ncgLLbNnL3WdsHTXgJIgwUEbUXSIq07rtpJRfVe8kN/gGgOzWMtlfkZdmelxd2OTBYVo bW7+QzV53nL0WBVlnwO2iSs33juUcq7+u0MzyT2XkYGbamfXuNu1tqZQCVOWGXDByBDXUu 2Y1Yz/KBTx7IvSzBtGvBA9wzulL5CZg= 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-428-A1rzR6SNMGKIqmDQpzlpfw-1; Tue, 30 May 2023 12:33:04 -0400 X-MC-Unique: A1rzR6SNMGKIqmDQpzlpfw-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 351CC8032FA; Tue, 30 May 2023 16:33:04 +0000 (UTC) Received: from merkur.redhat.com (unknown [10.39.194.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id 78363C154D2; Tue, 30 May 2023 16:33:03 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, richard.henderson@linaro.org, qemu-devel@nongnu.org Subject: [PULL 18/32] block/export: wait for vhost-user-blk requests when draining Date: Tue, 30 May 2023 18:32:25 +0200 Message-Id: <20230530163239.576632-19-kwolf@redhat.com> In-Reply-To: <20230530163239.576632-1-kwolf@redhat.com> References: <20230530163239.576632-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.167, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 From: Stefan Hajnoczi Each vhost-user-blk request runs in a coroutine. When the BlockBackend enters a drained section we need to enter a quiescent state. Currently any in-flight requests race with bdrv_drained_begin() because it is unaware of vhost-user-blk requests. When blk_co_preadv/pwritev()/etc returns it wakes the bdrv_drained_begin() thread but vhost-user-blk request processing has not yet finished. The request coroutine continues executing while the main loop thread thinks it is in a drained section. One example where this is unsafe is for blk_set_aio_context() where bdrv_drained_begin() is called before .aio_context_detached() and .aio_context_attach(). If request coroutines are still running after bdrv_drained_begin(), then the AioContext could change underneath them and they race with new requests processed in the new AioContext. This could lead to virtqueue corruption, for example. (This example is theoretical, I came across this while reading the code and have not tried to reproduce it.) It's easy to make bdrv_drained_begin() wait for in-flight requests: add a .drained_poll() callback that checks the VuServer's in-flight counter. VuServer just needs an API that returns true when there are requests in flight. The in-flight counter needs to be atomic. Signed-off-by: Stefan Hajnoczi Reviewed-by: Kevin Wolf Message-Id: <20230516190238.8401-7-stefanha@redhat.com> Signed-off-by: Kevin Wolf --- include/qemu/vhost-user-server.h | 4 +++- block/export/vhost-user-blk-server.c | 13 +++++++++++++ util/vhost-user-server.c | 18 ++++++++++++------ 3 files changed, 28 insertions(+), 7 deletions(-) diff --git a/include/qemu/vhost-user-server.h b/include/qemu/vhost-user-server.h index bc0ac9ddb6..b1c1cda886 100644 --- a/include/qemu/vhost-user-server.h +++ b/include/qemu/vhost-user-server.h @@ -40,8 +40,9 @@ typedef struct { int max_queues; const VuDevIface *vu_iface; + unsigned int in_flight; /* atomic */ + /* Protected by ctx lock */ - unsigned int in_flight; bool wait_idle; VuDev vu_dev; QIOChannel *ioc; /* The I/O channel with the client */ @@ -62,6 +63,7 @@ void vhost_user_server_stop(VuServer *server); void vhost_user_server_inc_in_flight(VuServer *server); void vhost_user_server_dec_in_flight(VuServer *server); +bool vhost_user_server_has_in_flight(VuServer *server); void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx); void vhost_user_server_detach_aio_context(VuServer *server); diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user-blk-server.c index 841acb36e3..f51a36a14f 100644 --- a/block/export/vhost-user-blk-server.c +++ b/block/export/vhost-user-blk-server.c @@ -272,7 +272,20 @@ static void vu_blk_exp_resize(void *opaque) vu_config_change_msg(&vexp->vu_server.vu_dev); } +/* + * Ensures that bdrv_drained_begin() waits until in-flight requests complete. + * + * Called with vexp->export.ctx acquired. + */ +static bool vu_blk_drained_poll(void *opaque) +{ + VuBlkExport *vexp = opaque; + + return vhost_user_server_has_in_flight(&vexp->vu_server); +} + static const BlockDevOps vu_blk_dev_ops = { + .drained_poll = vu_blk_drained_poll, .resize_cb = vu_blk_exp_resize, }; diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c index 1622f8cfb3..68c3bf162f 100644 --- a/util/vhost-user-server.c +++ b/util/vhost-user-server.c @@ -78,17 +78,23 @@ static void panic_cb(VuDev *vu_dev, const char *buf) void vhost_user_server_inc_in_flight(VuServer *server) { assert(!server->wait_idle); - server->in_flight++; + qatomic_inc(&server->in_flight); } void vhost_user_server_dec_in_flight(VuServer *server) { - server->in_flight--; - if (server->wait_idle && !server->in_flight) { - aio_co_wake(server->co_trip); + if (qatomic_fetch_dec(&server->in_flight) == 1) { + if (server->wait_idle) { + aio_co_wake(server->co_trip); + } } } +bool vhost_user_server_has_in_flight(VuServer *server) +{ + return qatomic_load_acquire(&server->in_flight) > 0; +} + static bool coroutine_fn vu_message_read(VuDev *vu_dev, int conn_fd, VhostUserMsg *vmsg) { @@ -192,13 +198,13 @@ static coroutine_fn void vu_client_trip(void *opaque) /* Keep running */ } - if (server->in_flight) { + if (vhost_user_server_has_in_flight(server)) { /* Wait for requests to complete before we can unmap the memory */ server->wait_idle = true; qemu_coroutine_yield(); server->wait_idle = false; } - assert(server->in_flight == 0); + assert(!vhost_user_server_has_in_flight(server)); vu_deinit(vu_dev); -- 2.40.1