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 5E7ABEED601 for ; Fri, 15 Sep 2023 14:52:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qhA37-0008Td-QU; Fri, 15 Sep 2023 10:44:01 -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 1qhA33-0008Ri-WE for qemu-devel@nongnu.org; Fri, 15 Sep 2023 10:43:58 -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 1qhA31-0004sb-SS for qemu-devel@nongnu.org; Fri, 15 Sep 2023 10:43:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694789035; 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=8v92/dCE8vJo+Zj2tGK8cRaYo68JxCK9b3JYXyq3YD4=; b=IoVCdUFlzHm2S83M4v+hL5LTcs9VVruCLEHz4XVy4/MrEp8WH2kTIKn63MmxCxEvjc67OS yRFiKifHjTfuVcQxsml0A3pmEyFQDTyW6s9mjloRdr65tytBxLq3CLEb0xyBErkiYZ2a/V dno3gOcZThGukg7Dd8W4sPnEmZv8OdI= 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-662-k5e6T_DuORe08b9i9BNVow-1; Fri, 15 Sep 2023 10:43:53 -0400 X-MC-Unique: k5e6T_DuORe08b9i9BNVow-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DFE7518162C1; Fri, 15 Sep 2023 14:43:52 +0000 (UTC) Received: from merkur.fritz.box (unknown [10.39.193.146]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4D5672026D4B; Fri, 15 Sep 2023 14:43:52 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [PULL 05/28] block: Introduce bdrv_schedule_unref() Date: Fri, 15 Sep 2023 16:43:21 +0200 Message-ID: <20230915144344.238596-6-kwolf@redhat.com> In-Reply-To: <20230915144344.238596-1-kwolf@redhat.com> References: <20230915144344.238596-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 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: -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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 bdrv_unref() is called by a lot of places that need to hold the graph lock (it naturally happens in the context of operations that change the graph). However, bdrv_unref() takes the graph writer lock internally, so it can't actually be called while already holding a graph lock without causing a deadlock. bdrv_unref() also can't just become GRAPH_WRLOCK because it drains the node before closing it, and draining requires that the graph is unlocked. The solution is to defer deleting the node until we don't hold the lock any more and draining is possible again. Note that keeping images open for longer than necessary can create problems, too: You can't open an image again before it is really closed (if image locking didn't prevent it, it would cause corruption). Reopening an image immediately happens at least during bdrv_open() and bdrv_co_create(). In order to solve this problem, make sure to run the deferred unref in bdrv_graph_wrunlock(), i.e. the first possible place where we can drain again. This is also why bdrv_schedule_unref() is marked GRAPH_WRLOCK. The output of iotest 051 is updated because the additional polling changes the order of HMP output, resulting in a new "(qemu)" prompt in the test output that was previously on a separate line and filtered out. Signed-off-by: Kevin Wolf Message-ID: <20230911094620.45040-6-kwolf@redhat.com> Reviewed-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- include/block/block-global-state.h | 1 + block.c | 17 +++++++++++++++++ block/graph-lock.c | 26 +++++++++++++++++++------- tests/qemu-iotests/051.pc.out | 6 +++--- 4 files changed, 40 insertions(+), 10 deletions(-) diff --git a/include/block/block-global-state.h b/include/block/block-global-state.h index f347199bff..e570799f85 100644 --- a/include/block/block-global-state.h +++ b/include/block/block-global-state.h @@ -224,6 +224,7 @@ void bdrv_img_create(const char *filename, const char *fmt, void bdrv_ref(BlockDriverState *bs); void no_coroutine_fn bdrv_unref(BlockDriverState *bs); void coroutine_fn no_co_wrapper bdrv_co_unref(BlockDriverState *bs); +void GRAPH_WRLOCK bdrv_schedule_unref(BlockDriverState *bs); void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child); BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs, BlockDriverState *child_bs, diff --git a/block.c b/block.c index 9029ddd9ff..c8ac7cfac4 100644 --- a/block.c +++ b/block.c @@ -7044,6 +7044,23 @@ void bdrv_unref(BlockDriverState *bs) } } +/* + * Release a BlockDriverState reference while holding the graph write lock. + * + * Calling bdrv_unref() directly is forbidden while holding the graph lock + * because bdrv_close() both involves polling and taking the graph lock + * internally. bdrv_schedule_unref() instead delays decreasing the refcount and + * possibly closing @bs until the graph lock is released. + */ +void bdrv_schedule_unref(BlockDriverState *bs) +{ + if (!bs) { + return; + } + aio_bh_schedule_oneshot(qemu_get_aio_context(), + (QEMUBHFunc *) bdrv_unref, bs); +} + struct BdrvOpBlocker { Error *reason; QLIST_ENTRY(BdrvOpBlocker) list; diff --git a/block/graph-lock.c b/block/graph-lock.c index f357a2c0b1..58a799065f 100644 --- a/block/graph-lock.c +++ b/block/graph-lock.c @@ -163,17 +163,29 @@ void bdrv_graph_wrlock(BlockDriverState *bs) void bdrv_graph_wrunlock(void) { GLOBAL_STATE_CODE(); - QEMU_LOCK_GUARD(&aio_context_list_lock); assert(qatomic_read(&has_writer)); + WITH_QEMU_LOCK_GUARD(&aio_context_list_lock) { + /* + * No need for memory barriers, this works in pair with + * the slow path of rdlock() and both take the lock. + */ + qatomic_store_release(&has_writer, 0); + + /* Wake up all coroutines that are waiting to read the graph */ + qemu_co_enter_all(&reader_queue, &aio_context_list_lock); + } + /* - * No need for memory barriers, this works in pair with - * the slow path of rdlock() and both take the lock. + * Run any BHs that were scheduled during the wrlock section and that + * callers might expect to have finished (in particular, this is important + * for bdrv_schedule_unref()). + * + * Do this only after restarting coroutines so that nested event loops in + * BHs don't deadlock if their condition relies on the coroutine making + * progress. */ - qatomic_store_release(&has_writer, 0); - - /* Wake up all coroutine that are waiting to read the graph */ - qemu_co_enter_all(&reader_queue, &aio_context_list_lock); + aio_bh_poll(qemu_get_aio_context()); } void coroutine_fn bdrv_graph_co_rdlock(void) diff --git a/tests/qemu-iotests/051.pc.out b/tests/qemu-iotests/051.pc.out index 4d4af5a486..7e10c5fa1b 100644 --- a/tests/qemu-iotests/051.pc.out +++ b/tests/qemu-iotests/051.pc.out @@ -169,11 +169,11 @@ QEMU_PROG: -device scsi-hd,drive=disk: Device needs media, but drive is empty Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device ide-hd,drive=disk,share-rw=on QEMU X.Y.Z monitor - type 'help' for more information -QEMU_PROG: -device ide-hd,drive=disk,share-rw=on: Cannot change iothread of active block backend +(qemu) QEMU_PROG: -device ide-hd,drive=disk,share-rw=on: Cannot change iothread of active block backend Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device virtio-blk-pci,drive=disk,share-rw=on QEMU X.Y.Z monitor - type 'help' for more information -QEMU_PROG: -device virtio-blk-pci,drive=disk,share-rw=on: Cannot change iothread of active block backend +(qemu) QEMU_PROG: -device virtio-blk-pci,drive=disk,share-rw=on: Cannot change iothread of active block backend Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device lsi53c895a,id=lsi0 -device scsi-hd,bus=lsi0.0,drive=disk,share-rw=on QEMU X.Y.Z monitor - type 'help' for more information @@ -185,7 +185,7 @@ QEMU X.Y.Z monitor - type 'help' for more information Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device virtio-blk-pci,drive=disk,iothread=thread0,share-rw=on QEMU X.Y.Z monitor - type 'help' for more information -QEMU_PROG: -device virtio-blk-pci,drive=disk,iothread=thread0,share-rw=on: Cannot change iothread of active block backend +(qemu) QEMU_PROG: -device virtio-blk-pci,drive=disk,iothread=thread0,share-rw=on: Cannot change iothread of active block backend Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device virtio-scsi,id=virtio-scsi1,iothread=thread0 -device scsi-hd,bus=virtio-scsi1.0,drive=disk,share-rw=on QEMU X.Y.Z monitor - type 'help' for more information -- 2.41.0