From nobody Sat Nov 23 21:19:46 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 173114748551129.73739426014845; Sat, 9 Nov 2024 02:18:05 -0800 (PST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t9iUl-00048p-4L; Sat, 09 Nov 2024 05:15:07 -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 1t9iUZ-0003tP-KL; Sat, 09 Nov 2024 05:14:58 -0500 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t9iUX-0007Wo-PQ; Sat, 09 Nov 2024 05:14:55 -0500 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id 5E322A13E9; Sat, 9 Nov 2024 13:13:49 +0300 (MSK) Received: from think4mjt.tls.msk.ru (mjtthink.wg.tls.msk.ru [192.168.177.146]) by tsrv.corpit.ru (Postfix) with ESMTP id 0A111167ED5; Sat, 9 Nov 2024 13:14:44 +0300 (MSK) From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Fiona Ebner , Vladimir Sementsov-Ogievskiy , Michael Tokarev Subject: [Stable-8.2.8 05/49] block/reqlist: allow adding overlapping requests Date: Sat, 9 Nov 2024 13:13:56 +0300 Message-Id: <20241109101443.312701-5-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.5 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1731147487162116600 Content-Type: text/plain; charset="utf-8" From: Fiona Ebner Allow overlapping request by removing the assert that made it impossible. There are only two callers: 1. block_copy_task_create() It already asserts the very same condition before calling reqlist_init_req(). 2. cbw_snapshot_read_lock() There is no need to have read requests be non-overlapping in copy-before-write when used for snapshot-access. In fact, there was no protection against two callers of cbw_snapshot_read_lock() calling reqlist_init_req() with overlapping ranges and this could lead to an assertion failure [1]. In particular, with the reproducer script below [0], two cbw_co_snapshot_block_status() callers could race, with the second calling reqlist_init_req() before the first one finishes and removes its conflicting request. [0]: > #!/bin/bash -e > dd if=3D/dev/urandom of=3D/tmp/disk.raw bs=3D1M count=3D1024 > ./qemu-img create /tmp/fleecing.raw -f raw 1G > ( > ./qemu-system-x86_64 --qmp stdio \ > --blockdev raw,node-name=3Dnode0,file.driver=3Dfile,file.filename=3D/tmp/= disk.raw \ > --blockdev raw,node-name=3Dnode1,file.driver=3Dfile,file.filename=3D/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=3Dexp0 -f raw= -r > nbdinfo --map 'nbd+unix:///exp0?socket=3D/tmp/nbd.socket' > done [1]: > #5 0x000071e5f0088eb2 in __GI___assert_fail (...) at ./assert/assert.c:1= 01 > #6 0x0000615285438017 in reqlist_init_req (...) at ../block/reqlist.c:23 > #7 0x00006152853e2d98 in cbw_snapshot_read_lock (...) at ../block/copy-b= efore-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 ../blo= ck/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 ../b= lock/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/blo= ck-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 Cc: qemu-stable@nongnu.org Suggested-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Fiona Ebner Message-Id: <20240712140716.517911-1-f.ebner@proxmox.com> Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Vladimir Sementsov-Ogievskiy (cherry picked from commit 6475155d519209c80fdda53e05130365aa769838) Signed-off-by: Michael Tokarev diff --git a/block/copy-before-write.c b/block/copy-before-write.c index 13972879b1..fd2f4c517e 100644 --- a/block/copy-before-write.c +++ b/block/copy-before-write.c @@ -65,7 +65,8 @@ typedef struct BDRVCopyBeforeWriteState { =20 /* * @frozen_read_reqs: current read requests for fleecing user in bs->f= ile - * node. These areas must not be rewritten by guest. + * node. These areas must not be rewritten by guest. There can be mult= iple + * overlapping read requests. */ BlockReqList frozen_read_reqs; =20 diff --git a/block/reqlist.c b/block/reqlist.c index 08cb57cfa4..098e807378 100644 --- a/block/reqlist.c +++ b/block/reqlist.c @@ -20,8 +20,6 @@ void reqlist_init_req(BlockReqList *reqs, BlockReq *req, int64_t offset, int64_t bytes) { - assert(!reqlist_find_conflict(reqs, offset, bytes)); - *req =3D (BlockReq) { .offset =3D offset, .bytes =3D bytes, --=20 2.39.5