From nobody Sat Dec 28 10:28:59 2024 Delivered-To: importer2@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+importer2=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 1720793280149176.20535847325402; Fri, 12 Jul 2024 07:08:00 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sSGwC-0006xy-Gm; Fri, 12 Jul 2024 10:07:52 -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 1sSGvv-0006M1-Tl; Fri, 12 Jul 2024 10:07:37 -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 1sSGvs-0008Tk-V4; Fri, 12 Jul 2024 10:07:35 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 55CBB473F7; Fri, 12 Jul 2024 16:07:23 +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 v2] block/reqlist: allow adding overlapping requests Date: Fri, 12 Jul 2024 16:07:16 +0200 Message-Id: <20240712140716.517911-1-f.ebner@proxmox.com> X-Mailer: git-send-email 2.39.2 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+importer2=patchew.org@nongnu.org; helo=lists.gnu.org; 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+importer2=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer2=patchew.org@nongnu.org X-ZM-MESSAGEID: 1720793282750116300 Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Vladimir Sementsov-Ogievskiy --- Changes in v2: * different approach, allowing overlapping requests for copy-before-write rather than waiting for them. block-copy already asserts there are no conflicts before adding a request. block/copy-before-write.c | 3 ++- block/reqlist.c | 2 -- 2 files changed, 2 insertions(+), 3 deletions(-) diff --git a/block/copy-before-write.c b/block/copy-before-write.c index 853e01a1eb..28f6a096cd 100644 --- a/block/copy-before-write.c +++ b/block/copy-before-write.c @@ -66,7 +66,8 @@ 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 2.39.2