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(unknown [2a02:6b8:b081:b423::1:3a]) by mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id bXTAnY0Fe0U0-EKYKT2em; Tue, 29 Apr 2025 14:33:41 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1745926421; bh=xkLZ1GZTOtbVQt+osR2ziS0pLuj2G7hrkNYOXSXAPIU=; h=Message-ID:Date:In-Reply-To:Cc:Subject:References:To:From; b=Fzp22hLmF6e9sWVdT93i+PxIw/x4FZP033Gw0a+8mTSPxLBvhWZPsoZwZasTxgMnW vD2aX0qxYhaxShfEwgxRcCcCdnvaIK34tJrOPmo4/g7jqMnyGIxE03pTWTgJ0RddOo 8QvA+zuD7INGa8b8Vm+H4Kp9bjaOC1F3w6AndIBE= Authentication-Results: mail-nwsmtp-smtp-corp-main-56.klg.yp-c.yandex.net; dkim=pass header.i=@yandex-team.ru From: Vladimir Sementsov-Ogievskiy To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Fiona Ebner , qemu-stable@nongnu.org, Vladimir Sementsov-Ogievskiy Subject: [PULL 3/5] block/reqlist: allow adding overlapping requests Date: Tue, 29 Apr 2025 14:33:28 +0300 Message-ID: <20250429113335.423535-7-vsementsov@yandex-team.ru> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250429113335.423535-1-vsementsov@yandex-team.ru> References: <20250429113335.423535-1-vsementsov@yandex-team.ru> 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=178.154.239.200; envelope-from=vsementsov@yandex-team.ru; helo=forwardcorp1d.mail.yandex.net 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, 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_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-ZohoMail-DKIM: pass (identity @yandex-team.ru) X-ZM-MESSAGEID: 1745926588431019100 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 --- 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 e835987e52..81afeff1c7 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 2.34.1