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[130.117.225.111]) by mx.google.com with ESMTPS id ffacd0b85a97d-482fbb44707si3954157f8f.352.2026.08.28.10.03.54 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 10:03:54 -0700 (PDT) Received-SPF: pass (google.com: domain of khorenko@virtuozzo.com designates 130.117.225.111 as permitted sender) client-ip=130.117.225.111; Authentication-Results: mx.google.com; dkim=pass header.i=@virtuozzo.com header.s=relay header.b=LHepzl3R; spf=pass (google.com: domain of khorenko@virtuozzo.com designates 130.117.225.111 as permitted sender) smtp.mailfrom=khorenko@virtuozzo.com; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=virtuozzo.com DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=Subject:From:Message-Id:Date:Content-Type: MIME-Version; bh=QpusKg6OqlBhjMI1PWeSURnfquqkJcsgE75HVQoohOY=; b=LHepzl3RSOiW gSF/C9EpG9rvMogAy40PZFlFZmSpMYO0oLJpYjgF2+jnHBsk/l7zcFJh+2ECcHqKk273sKqBcBElw o+EggwoQbYM1hFadTB4OXQFjfZt8u5p1X+wD2ftugfjE5TBnyKXgYDnsD/BXkarkINSVo90fFhhsf 7nbBJjEZuz9NzHuxNm35+4O0WWaAE15qYXTX31nb+gFhxnsXfreOXmEEfI3oSYXOdKlxTEBKU4UHB vi3gLbFLwNwPlcPpbTmQ5SUpwoPfWqHi6sOMaG8SmOUpsmwXS2YxAwvfgs4QqaoQOaXXIIJVlAeag 9HOg95gsuLiE4qyPOzFavQ==; Received: from ch-demo-asa.virtuozzo.com ([130.117.225.8] helo=f0.sw.ru) by relay.virtuozzo.com with esmtps (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1wzzxM-008duC-0z; Fri, 28 Aug 2026 19:03:50 +0200 Received: from f0.sw.ru (localhost [127.0.0.1]) by f0.sw.ru (8.18.1/8.18.1/Debian-2) with ESMTP id 67SH3rt41064093; Fri, 28 Aug 2026 19:03:53 +0200 Received: (from kostja@localhost) by f0.sw.ru (8.18.1/8.18.1/Submit) id 67SH3rYA1064092; Fri, 28 Aug 2026 19:03:53 +0200 Date: Fri, 28 Aug 2026 19:03:53 +0200 Message-Id: <202608281703.67SH3rYA1064092@f0.sw.ru> X-Authentication-Warning: f0.sw.ru: kostja set sender to khorenko@virtuozzo.com using -f From: Konstantin Khorenko To: Andrey Zhadchenko In-Reply-to: <20260827160619.303398-6-andrey.zhadchenko@virtuozzo.com> X-OZ-Fwd: true Cc: OpenVZ devel Subject: Re: [Devel] [PATCH RHEL10 COMMIT] drivers/md/dm-qcow2: never trigger COW or allocation on discard X-BeenThere: devel@openvz.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: OpenVZ development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: devel-bounces@openvz.org Errors-To: devel-bounces@openvz.org The commit is pushed to "branch-rh10-6.12.0-211.39.1.16.x.vz10-ovz" and will appear at git@bitbucket.org:openvz/vzkernel.git after rh10-6.12.0-211.39.1.16.11.vz10 ------> commit a8c956f2c96894e7d44ff7010204eb415d8dd123 Author: Andrey Zhadchenko Date: Thu Aug 27 19:06:13 2026 +0300 drivers/md/dm-qcow2: never trigger COW or allocation on discard In handle_metadata() the partial cluster discard fallback is checked only after the COW branches. As a result a discard, whose range touches a shared (snapshot or compressed) cluster or crosses an unmapped unit border over a backing file, is routed into the data COW machinery. COW then tries to submit the discard payload as a data write, but discard qios carry no bvec array: the iov_iter is built from garbage, which triggers the WARN_ON() in __submit_rw_mapped() and writes random kernel memory into the COW'ed cluster. Check for discard before the COW branches: discard is advisory and carries no data, so it must never COW or allocate. End discard early while handling metadata if possible. Otherwise do discard operations before COWs. Feature: dm-qcow2: block device over QCOW2 files driver https://virtuozzo.atlassian.net/browse/VSTOR-139406 Signed-off-by: Andrey Zhadchenko Reviewed-by: Pavel Tikhomirov Reviewed-by: Vasileios Almpanis Reviewed-by: Konstantin Khorenko --- drivers/md/dm-qcow2-map.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c index 8cdacaa57d3d5..90229cdb5b006 100644 --- a/drivers/md/dm-qcow2-map.c +++ b/drivers/md/dm-qcow2-map.c @@ -3431,9 +3431,18 @@ static int handle_metadata(struct qcow2 *qcow2, struct qio **qio, /* Nothing to COW or L1 is mapped exactly once */ qio_endio(*qio); ret = 0; - } else if (unlikely(op_is_discard((*qio)->bi_op)) && - qio_discard_updates_metadata(qcow2, *qio, map)) { - ret = prepare_cluster_discard(qcow2, qio, map); + } else if (unlikely(op_is_discard((*qio)->bi_op))) { + /* + * Discard carries no data and is advisory. If it does not + * trigger metadata changes or to-be-discarded cluster + * is not present, end early. + */ + if (qio_discard_updates_metadata(qcow2, *qio, map)) { + ret = prepare_cluster_discard(qcow2, qio, map); + } else if (!map->data_clu_alloced || map->clu_is_cow) { + qio_endio(*qio); + ret = 0; + } } else if (write && (!qio_is_fully_alloced(qcow2, *qio, map) || map->clu_is_cow)) { if (map->clu_is_cow) { @@ -3449,13 +3458,6 @@ static int handle_metadata(struct qcow2 *qcow2, struct qio **qio, */ map->backing_file_cow = true; ret = prepare_l1l2_replace(qcow2, *qio, map); - } else if (unlikely(op_is_discard((*qio)->bi_op) && - (map->level & L2_LEVEL))) { - if (!map->data_clu_alloced) { - qio_endio(*qio); - ret = 0; - } - /* Otherwise issue_discard(). */ } else { /* Wants L1 or L2 entry allocation */ ret = prepare_l1l2_allocation(qcow2, *qio, map); @@ -3569,8 +3571,8 @@ static void process_one_qio(struct qcow2 *qcow2, struct qio *qio) write = op_is_write(qio->bi_op); - /* Discard with prepared metadata update, see prepare_cluster_discard() */ - if (unlikely(qio->flags & QIO_IS_DISCARD_FL)) { + /* Process discard early. Don't do COW just to discard */ + if (unlikely(op_is_discard(qio->bi_op))) { issue_discard(&map, qio); return; } @@ -3588,8 +3590,6 @@ static void process_one_qio(struct qcow2 *qcow2, struct qio *qio) submit_read_whole_cow_clu(&map, qio); else if (unlikely(map.clu_is_cow || map.backing_file_cow)) submit_read_sliced_cow_clu(&map, qio); - else if (unlikely(op_is_discard(qio->bi_op))) - issue_discard(&map, qio); else perform_rw_mapped(&map, qio); } _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel