From patchwork Thu Jul 11 13:36:52 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fiona Ebner X-Patchwork-Id: 13730734 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 392B1C3DA41 for ; Thu, 11 Jul 2024 13:38:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sRtyr-0006Pm-5J; Thu, 11 Jul 2024 09:37:05 -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 1sRtyo-0006En-OA; Thu, 11 Jul 2024 09:37:02 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sRtyl-0005uk-Sc; Thu, 11 Jul 2024 09:37:02 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 922044732C; Thu, 11 Jul 2024 15:36:56 +0200 (CEST) From: Fiona Ebner To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, qemu-stable@nongnu.org, hreitz@redhat.com, kwolf@redhat.com, vsementsov@yandex-team.ru, jsnow@redhat.com Subject: [PATCH] block/copy-before-write: wait for conflicts when read locking to avoid assertion failure Date: Thu, 11 Jul 2024 15:36:52 +0200 Message-Id: <20240711133652.589770-1-f.ebner@proxmox.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Received-SPF: pass client-ip=94.136.29.106; envelope-from=f.ebner@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, 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 There is no protection against two callers of cbw_snapshot_read_lock() calling reqlist_init_req() with overlapping ranges, and reqlist_init_req() asserts that there are no conflicting requests. In particular, two cbw_co_snapshot_block_status() callers can race, with the second calling reqlist_init_req() before the first one finishes and removes its conflicting request, leading to an assertion failure. Reproducer script [0] and backtrace [1] are attached below. [0]: > #!/bin/bash -e > dd if=/dev/urandom of=/tmp/disk.raw bs=1M count=1024 > ./qemu-img create /tmp/fleecing.raw -f raw 1G > ( > ./qemu-system-x86_64 --qmp stdio \ > --blockdev raw,node-name=node0,file.driver=file,file.filename=/tmp/disk.raw \ > --blockdev raw,node-name=node1,file.driver=file,file.filename=/tmp/fleecing.raw \ > < {"execute": "qmp_capabilities"} > {"execute": "blockdev-add", "arguments": { "driver": "copy-before-write", "file": "node0", "target": "node1", "node-name": "node3" } } > {"execute": "blockdev-add", "arguments": { "driver": "snapshot-access", "file": "node3", "node-name": "snap0" } } > {"execute": "nbd-server-start", "arguments": {"addr": { "type": "unix", "data": { "path": "/tmp/nbd.socket" } } } } > {"execute": "block-export-add", "arguments": {"id": "exp0", "node-name": "snap0", "type": "nbd", "name": "exp0"}} > EOF > ) & > sleep 5 > while true; do > ./qemu-nbd -d /dev/nbd0 > ./qemu-nbd -c /dev/nbd0 nbd:unix:/tmp/nbd.socket:exportname=exp0 -f raw -r > nbdinfo --map 'nbd+unix:///exp0?socket=/tmp/nbd.socket' > done [1]: > #5 0x000071e5f0088eb2 in __GI___assert_fail (...) at ./assert/assert.c:101 > #6 0x0000615285438017 in reqlist_init_req (...) at ../block/reqlist.c:23 > #7 0x00006152853e2d98 in cbw_snapshot_read_lock (...) at ../block/copy-before-write.c:237 > #8 0x00006152853e3068 in cbw_co_snapshot_block_status (...) at ../block/copy-before-write.c:304 > #9 0x00006152853f4d22 in bdrv_co_snapshot_block_status (...) at ../block/io.c:3726 > #10 0x000061528543a63e in snapshot_access_co_block_status (...) at ../block/snapshot-access.c:48 > #11 0x00006152853f1a0a in bdrv_co_do_block_status (...) at ../block/io.c:2474 > #12 0x00006152853f2016 in bdrv_co_common_block_status_above (...) at ../block/io.c:2652 > #13 0x00006152853f22cf in bdrv_co_block_status_above (...) at ../block/io.c:2732 > #14 0x00006152853d9a86 in blk_co_block_status_above (...) at ../block/block-backend.c:1473 > #15 0x000061528538da6c in blockstatus_to_extents (...) at ../nbd/server.c:2374 > #16 0x000061528538deb1 in nbd_co_send_block_status (...) at ../nbd/server.c:2481 > #17 0x000061528538f424 in nbd_handle_request (...) at ../nbd/server.c:2978 > #18 0x000061528538f906 in nbd_trip (...) at ../nbd/server.c:3121 > #19 0x00006152855a7caf in coroutine_trampoline (...) at ../util/coroutine-ucontext.c:175 Signed-off-by: Fiona Ebner --- block/copy-before-write.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/copy-before-write.c b/block/copy-before-write.c index 853e01a1eb..376ff3f3e1 100644 --- a/block/copy-before-write.c +++ b/block/copy-before-write.c @@ -234,6 +234,7 @@ cbw_snapshot_read_lock(BlockDriverState *bs, int64_t offset, int64_t bytes, *req = (BlockReq) {.offset = -1, .bytes = -1}; *file = s->target; } else { + reqlist_wait_all(&s->frozen_read_reqs, offset, bytes, &s->lock); reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes); *file = bs->file; }