From patchwork Mon Nov 7 15:13:21 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hanna Czenczek X-Patchwork-Id: 13034562 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 243B2C4332F for ; Mon, 7 Nov 2022 15:15:23 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1os3oe-0001sp-C9; Mon, 07 Nov 2022 10:13:36 -0500 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 1os3oc-0001rR-Em for qemu-devel@nongnu.org; Mon, 07 Nov 2022 10:13:34 -0500 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 1os3oa-00071K-Td for qemu-devel@nongnu.org; Mon, 07 Nov 2022 10:13:34 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667834012; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Uq8qwPDvdYV9JH6DyNZb7wffdpZ/MNjI6/bR90lZT68=; b=CqkoELodp0a8q6iuB8YePtI7dV1rpgBPY+yiS7XesdibiN3z3ByY9AWtLrQQcg5hGWoboI b8Syu3TbX3wzKwikSMNafeNSzY52S93wM+45u2wiEbPiI90PITARwtoRfX1DLzSS9N2EkS G45bR6bU7wg2YHhWeiYc4QKWwYPNz8Q= 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-609-IiKkCnB0NMGE9Z109loMrQ-1; Mon, 07 Nov 2022 10:13:29 -0500 X-MC-Unique: IiKkCnB0NMGE9Z109loMrQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 82CE6101E985; Mon, 7 Nov 2022 15:13:28 +0000 (UTC) Received: from localhost (unknown [10.39.194.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2D6A51121315; Mon, 7 Nov 2022 15:13:28 +0000 (UTC) From: Hanna Reitz To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Hanna Reitz , Kevin Wolf , Stefan Hajnoczi Subject: [PATCH v2 3/3] block: Start/end drain on correct AioContext Date: Mon, 7 Nov 2022 16:13:21 +0100 Message-Id: <20221107151321.211175-4-hreitz@redhat.com> In-Reply-To: <20221107151321.211175-1-hreitz@redhat.com> References: <20221107151321.211175-1-hreitz@redhat.com> MIME-Version: 1.0 Content-type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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 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 bdrv_parent_drained_{begin,end}_single() are supposed to operate on the parent, not on the child, so they should not attempt to get the context to poll from the child but the parent instead. BDRV_POLL_WHILE(c->bs) does get the context from the child, so we should replace it with AIO_WAIT_WHILE() on the parent's context instead. This problem becomes apparent when bdrv_replace_child_noperm() invokes bdrv_parent_drained_end_single() after removing a child from a subgraph that is in an I/O thread. By the time bdrv_parent_drained_end_single() is called, child->bs is NULL, and so BDRV_POLL_WHILE(c->bs, ...) will poll the main loop instead of the I/O thread; but anything that bdrv_parent_drained_end_single_no_poll() may have scheduled is going to want to run in the I/O thread, but because we poll the main loop, the I/O thread is never unpaused, and nothing is run, resulting in a deadlock. Closes: https://gitlab.com/qemu-project/qemu/-/issues/1215 Reviewed-by: Kevin Wolf Signed-off-by: Hanna Reitz --- block/io.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/block/io.c b/block/io.c index 34b30e304e..b9424024f9 100644 --- a/block/io.c +++ b/block/io.c @@ -71,9 +71,10 @@ static void bdrv_parent_drained_end_single_no_poll(BdrvChild *c, void bdrv_parent_drained_end_single(BdrvChild *c) { int drained_end_counter = 0; + AioContext *ctx = bdrv_child_get_parent_aio_context(c); IO_OR_GS_CODE(); bdrv_parent_drained_end_single_no_poll(c, &drained_end_counter); - BDRV_POLL_WHILE(c->bs, qatomic_read(&drained_end_counter) > 0); + AIO_WAIT_WHILE(ctx, qatomic_read(&drained_end_counter) > 0); } static void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore, @@ -116,13 +117,14 @@ static bool bdrv_parent_drained_poll(BlockDriverState *bs, BdrvChild *ignore, void bdrv_parent_drained_begin_single(BdrvChild *c, bool poll) { + AioContext *ctx = bdrv_child_get_parent_aio_context(c); IO_OR_GS_CODE(); c->parent_quiesce_counter++; if (c->klass->drained_begin) { c->klass->drained_begin(c); } if (poll) { - BDRV_POLL_WHILE(c->bs, bdrv_parent_drained_poll_single(c)); + AIO_WAIT_WHILE(ctx, bdrv_parent_drained_poll_single(c)); } }