From patchwork Thu Apr 20 11:37:18 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13218575 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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 489CDC77B73 for ; Thu, 20 Apr 2023 11:38:47 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.524136.814818 (Exim 4.92) (envelope-from ) id 1ppScX-0003bC-Fz; Thu, 20 Apr 2023 11:38:37 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 524136.814818; Thu, 20 Apr 2023 11:38:37 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ppScX-0003b2-CU; Thu, 20 Apr 2023 11:38:37 +0000 Received: by outflank-mailman (input) for mailman id 524136; Thu, 20 Apr 2023 11:38:35 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ppScV-0001nK-Cf for xen-devel@lists.xenproject.org; Thu, 20 Apr 2023 11:38:35 +0000 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id e0e935c8-df6f-11ed-8611-37d641c3527e; Thu, 20 Apr 2023 13:38:33 +0200 (CEST) Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-135-Ag2DDzwlMYCeNFYqlalYBQ-1; Thu, 20 Apr 2023 07:38:29 -0400 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 2BF321C08976; Thu, 20 Apr 2023 11:38:28 +0000 (UTC) Received: from localhost (unknown [10.39.193.254]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7FBD1C16024; Thu, 20 Apr 2023 11:38:27 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: e0e935c8-df6f-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681990712; 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=+bLg6uTzP7Qgt6lQ3xKdY10AY3Nt3xLke1uGL1u9ShU=; b=APo/zLq4WecTRndfbXeZ96HbecFzPnDdiY2zExDS7D9BF/bda666K4lZry2iK6ZOkYU2sL LbuBZ1r6QfAxuFkKoC/mcqi+pJkT2zRgKOmuHZ7qP9BFmTnBu5CZ3g/Hoorvxf/Xc3TnQ5 nQG3NSL+EgmroC5WSo20NjdZ/XTOtOg= X-MC-Unique: Ag2DDzwlMYCeNFYqlalYBQ-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Peter Lieven , Stefan Hajnoczi , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Xie Yongji , Juan Quintela , qemu-block@nongnu.org, Eduardo Habkost , Richard Henderson , David Woodhouse , Stefan Weil , Fam Zheng , Julia Suvorova , Ronnie Sahlberg , xen-devel@lists.xenproject.org, Hanna Reitz , "Dr. David Alan Gilbert" , eesposit@redhat.com, Kevin Wolf , Marcel Apfelbaum , Stefano Stabellini , Paul Durrant , Aarushi Mehta , "Michael S. Tsirkin" , Anthony Perard , "Richard W.M. Jones" , Coiby Xu , Stefano Garzarella Subject: [PATCH v3 06/20] block/export: wait for vhost-user-blk requests when draining Date: Thu, 20 Apr 2023 07:37:18 -0400 Message-Id: <20230420113732.336620-7-stefanha@redhat.com> In-Reply-To: <20230420113732.336620-1-stefanha@redhat.com> References: <20230420113732.336620-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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 --- include/qemu/vhost-user-server.h | 4 +++- block/export/vhost-user-blk-server.c | 19 +++++++++++++++++++ util/vhost-user-server.c | 14 ++++++++++---- 3 files changed, 32 insertions(+), 5 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 e93f2ed6b4..dbf5207162 100644 --- a/block/export/vhost-user-blk-server.c +++ b/block/export/vhost-user-blk-server.c @@ -254,6 +254,22 @@ static void vu_blk_exp_request_shutdown(BlockExport *exp) vhost_user_server_stop(&vexp->vu_server); } +/* + * 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, +}; + static int vu_blk_exp_create(BlockExport *exp, BlockExportOptions *opts, Error **errp) { @@ -292,6 +308,7 @@ static int vu_blk_exp_create(BlockExport *exp, BlockExportOptions *opts, vu_blk_initialize_config(blk_bs(exp->blk), &vexp->blkcfg, logical_block_size, num_queues); + blk_set_dev_ops(exp->blk, &vu_blk_dev_ops, vexp); blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach, vexp); @@ -299,6 +316,7 @@ static int vu_blk_exp_create(BlockExport *exp, BlockExportOptions *opts, num_queues, &vu_blk_iface, errp)) { blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach, vexp); + blk_set_dev_ops(exp->blk, NULL, NULL); g_free(vexp->handler.serial); return -EADDRNOTAVAIL; } @@ -312,6 +330,7 @@ static void vu_blk_exp_delete(BlockExport *exp) blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach, vexp); + blk_set_dev_ops(exp->blk, NULL, NULL); g_free(vexp->handler.serial); } diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c index 1622f8cfb3..2e6b640050 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) {