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.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 900A8C77B7E for ; Tue, 2 May 2023 15:43:29 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.528732.822245 (Exim 4.92) (envelope-from ) id 1pts9j-0007ca-IS; Tue, 02 May 2023 15:43:07 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 528732.822245; Tue, 02 May 2023 15:43:07 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1pts9j-0007cT-Fi; Tue, 02 May 2023 15:43:07 +0000 Received: by outflank-mailman (input) for mailman id 528732; Tue, 02 May 2023 15:43:05 +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 1pts9h-0007cN-OJ for xen-devel@lists.xenproject.org; Tue, 02 May 2023 15:43:05 +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 0599a117-e900-11ed-8611-37d641c3527e; Tue, 02 May 2023 17:43:03 +0200 (CEST) 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-647-kgZznv_pOqGm5hBR5_5Thg-1; Tue, 02 May 2023 11:42:57 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 24D3FA0F389; Tue, 2 May 2023 15:42:56 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.211]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71F17404E4AD; Tue, 2 May 2023 15:42:52 +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: 0599a117-e900-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683042181; 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=xl8B7Hoag5VEXFozvo4Ia9rRJMwFaCM8mAYKxZI+zJE=; b=BF7/GlcHdRmWRANPu3gFbydxQelORZTeHJo9gofW36xmZJUiF2/HuxZfFn6728srGVGeoF diygddfxRJGOjq9KW+GrOqc9n0fOMO10Ey6TwDrx6QEZBIime9UyP+qzaD/Li9ve2vDZ0U F+qAPzgn2dkxMKuuV/GubBgQrclKbCE= X-MC-Unique: kgZznv_pOqGm5hBR5_5Thg-1 Date: Tue, 2 May 2023 17:42:51 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Juan Quintela , Julia Suvorova , xen-devel@lists.xenproject.org, eesposit@redhat.com, Richard Henderson , Fam Zheng , "Michael S. Tsirkin" , Coiby Xu , David Woodhouse , Marcel Apfelbaum , Peter Lieven , Paul Durrant , "Richard W.M. Jones" , qemu-block@nongnu.org, Stefano Garzarella , Anthony Perard , Stefan Weil , Xie Yongji , Paolo Bonzini , Aarushi Mehta , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Eduardo Habkost , Stefano Stabellini , Hanna Reitz , Ronnie Sahlberg Subject: Re: [PATCH v4 06/20] block/export: wait for vhost-user-blk requests when draining Message-ID: References: <20230425172716.1033562-1-stefanha@redhat.com> <20230425172716.1033562-7-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230425172716.1033562-7-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Am 25.04.2023 um 19:27 hat Stefan Hajnoczi geschrieben: > 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 | 16 ++++++++++++++++ > util/vhost-user-server.c | 14 ++++++++++---- > 3 files changed, 29 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 841acb36e3..092b86aae4 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, > }; You're adding a new function pointer to an existing BlockDevOps... > @@ -314,6 +327,7 @@ 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); > > blk_set_dev_ops(exp->blk, &vu_blk_dev_ops, vexp); ..but still add a second blk_set_dev_ops(). Maybe a bad merge conflict resolution with commit ca858a5fe94? > @@ -323,6 +337,7 @@ 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; > } > @@ -336,6 +351,7 @@ 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); > } These two hunks are then probably already fixes for ca858a5fe94 and should be a separate patch if so. > 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; > +} > + Any reason why you left the server->in_flight accesses in vu_client_trip() non-atomic? Kevin