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 58406C77B7E for ; Tue, 2 May 2023 16:05:23 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ptsUd-0000cU-J3; Tue, 02 May 2023 12:04:44 -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 1ptsUZ-0000aZ-SB for qemu-devel@nongnu.org; Tue, 02 May 2023 12:04:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ptsUX-0007k2-NF for qemu-devel@nongnu.org; Tue, 02 May 2023 12:04:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683043476; 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=ErZ2aQ2HUcNIqx2OSDpVI+Y5PzprxF1vRVAtic0RH4k=; b=EgkcipQjNz4YPm2gSa1mi88Ay8gP+OaCYderdbuazMZvrv5e6e0o1UXy4P8GSWvo03TXRm Euqy6BYSHb1d+syBjtYYno32mfBCuQQRXXjDTr/kXIJWu0TkMiGu8kFF0squJIAdcRc1D9 VO1E1uPzrIZreMZyPgHCd01XRsL5q7A= 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-199-NtVPAAg0PAGoLecNFhMJ8Q-1; Tue, 02 May 2023 12:04:32 -0400 X-MC-Unique: NtVPAAg0PAGoLecNFhMJ8Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 506A218E5380; Tue, 2 May 2023 16:04:30 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.211]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 77F2C1410F24; Tue, 2 May 2023 16:04:25 +0000 (UTC) Date: Tue, 2 May 2023 18:04:24 +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 07/20] block/export: stop using is_external in vhost-user-blk server Message-ID: References: <20230425172716.1033562-1-stefanha@redhat.com> <20230425172716.1033562-8-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230425172716.1033562-8-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; 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=-0.171, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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 Am 25.04.2023 um 19:27 hat Stefan Hajnoczi geschrieben: > vhost-user activity must be suspended during bdrv_drained_begin/end(). > This prevents new requests from interfering with whatever is happening > in the drained section. > > Previously this was done using aio_set_fd_handler()'s is_external > argument. In a multi-queue block layer world the aio_disable_external() > API cannot be used since multiple AioContext may be processing I/O, not > just one. > > Switch to BlockDevOps->drained_begin/end() callbacks. > > Signed-off-by: Stefan Hajnoczi > --- > block/export/vhost-user-blk-server.c | 43 ++++++++++++++-------------- > util/vhost-user-server.c | 10 +++---- > 2 files changed, 26 insertions(+), 27 deletions(-) > > diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user-blk-server.c > index 092b86aae4..d20f69cd74 100644 > --- a/block/export/vhost-user-blk-server.c > +++ b/block/export/vhost-user-blk-server.c > @@ -208,22 +208,6 @@ static const VuDevIface vu_blk_iface = { > .process_msg = vu_blk_process_msg, > }; > > -static void blk_aio_attached(AioContext *ctx, void *opaque) > -{ > - VuBlkExport *vexp = opaque; > - > - vexp->export.ctx = ctx; > - vhost_user_server_attach_aio_context(&vexp->vu_server, ctx); > -} > - > -static void blk_aio_detach(void *opaque) > -{ > - VuBlkExport *vexp = opaque; > - > - vhost_user_server_detach_aio_context(&vexp->vu_server); > - vexp->export.ctx = NULL; > -} So for changing the AioContext, we now rely on the fact that the node to be changed is always drained, so the drain callbacks implicitly cover this case, too? > static void > vu_blk_initialize_config(BlockDriverState *bs, > struct virtio_blk_config *config, > @@ -272,6 +256,25 @@ static void vu_blk_exp_resize(void *opaque) > vu_config_change_msg(&vexp->vu_server.vu_dev); > } > > +/* Called with vexp->export.ctx acquired */ > +static void vu_blk_drained_begin(void *opaque) > +{ > + VuBlkExport *vexp = opaque; > + > + vhost_user_server_detach_aio_context(&vexp->vu_server); > +} Compared to the old code, we're losing the vexp->export.ctx = NULL. This is correct at this point because after drained_begin we still keep processing requests until we arrive at a quiescent state. However, if we detach the AioContext because we're deleting the iothread, won't we end up with a dangling pointer in vexp->export.ctx? Or can we be certain that nothing interesting happens before drained_end updates it with a new valid pointer again? Kevin