From nobody Tue Apr 7 17:16:30 2026 Received: from m16.mail.163.com (m16.mail.163.com [117.135.210.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9DD58333725; Fri, 27 Feb 2026 05:42:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=117.135.210.3 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772170980; cv=none; b=jdwliek1ewMccgM9CgYbsIDww6mbn1gSKQXXUu1CQWqRsHhZgItnoV65hmJWXMMarSOX4ZI1Mtc+ppRzkWvbXSSPtpMKCwWiZc9bPdI9GOIiiuE+ObRNRf8rHpVmp2YjCftQGMXc9BSsn1T2XvGCoE5Djj0aId9oxcoyNy9+3j8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772170980; c=relaxed/simple; bh=UEFYHfqMWFpDiSnQ2ZxTCTNSUX+TOxmPK4EN9foOkkY=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=r1qszyLYV29PjzWZlfoks2QDiETcUVKKnhj5Rv2h8pi2ryWwwBDoQTSo1I+N+En/86Myvy6zBKeW8Cesnrqfm2o+9e7+F+mo93v/eGbyaB6YQgKV+w46tNZgNJpKk9dGoY3ax8Z6EEW7ssoXdgeA2s77HSmW5Oikn/a59YY72Eo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=QZiHFZH/; arc=none smtp.client-ip=117.135.210.3 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="QZiHFZH/" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=3P V+nFQl72KJIa+ap8G2QRJx7vnWLumEZixOEyBdyH4=; b=QZiHFZH/nJwoGVezg2 Jc40EX6AD7MmmYuL3z0mT8Ralhtk7rARLwtLodMTgpAZcYQB13WE0oy1KWkThqly BQzU+Lhdm7Ssydu8++48Dr5bSuDkTHG3EkHiqW0J9qSUc1PoNjgH6TRKFoete5Cs LWtzCn20QA7XlS3hSsPPv1mgs= Received: from pek-lpg-core5.wrs.com (unknown []) by gzsmtp2 (Coremail) with SMTP id PSgvCgD3H+q_LqFpzaxOTQ--.788S2; Fri, 27 Feb 2026 13:42:24 +0800 (CST) From: Robert Garcia To: stable@vger.kernel.org, Han Guangjiang Cc: Jens Axboe , Robert Garcia , Liang Jie , Yu Kuai , Tejun Heo , Josef Bacik , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.12.y] blk-throttle: fix access race during throttle policy activation Date: Fri, 27 Feb 2026 13:42:23 +0800 Message-Id: <20260227054223.1552598-1-rob_garcia@163.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: PSgvCgD3H+q_LqFpzaxOTQ--.788S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxtF4rCr1DWF4DJrWxuF1UGFg_yoWxJr45pr W3WF15Kr4vqFsrWF45Jw43XFWrKw4kAay5G393J3yayF4j9w18t3WrAry8ArW8AFs3GF43 Ar4Dtr40kF1UCaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07UxnYwUUUUU= X-CM-SenderInfo: 5uresw5dufxti6rwjhhfrp/xtbDAQB+6WmhLsC-HAAA3T Content-Type: text/plain; charset="utf-8" From: Han Guangjiang [ Upstream commit bd9fd5be6bc0836820500f68fff144609fbd85a9 ] On repeated cold boots we occasionally hit a NULL pointer crash in blk_should_throtl() when throttling is consulted before the throttle policy is fully enabled for the queue. Checking only q->td !=3D NULL is insufficient during early initialization, so blkg_to_pd() for the throttle policy can still return NULL and blkg_to_tg() becomes NULL, which later gets dereferenced. Unable to handle kernel NULL pointer dereference at virtual address 0000000000000156 ... pc : submit_bio_noacct+0x14c/0x4c8 lr : submit_bio_noacct+0x48/0x4c8 sp : ffff800087f0b690 x29: ffff800087f0b690 x28: 0000000000005f90 x27: ffff00068af393c0 x26: 0000000000080000 x25: 000000000002fbc0 x24: ffff000684ddcc70 x23: 0000000000000000 x22: 0000000000000000 x21: 0000000000000000 x20: 0000000000080000 x19: ffff000684ddcd08 x18: ffffffffffffffff x17: 0000000000000000 x16: ffff80008132a550 x15: 0000ffff98020fff x14: 0000000000000000 x13: 1fffe000d11d7021 x12: ffff000688eb810c x11: ffff00077ec4bb80 x10: ffff000688dcb720 x9 : ffff80008068ef60 x8 : 00000a6fb8a86e85 x7 : 000000000000111e x6 : 0000000000000002 x5 : 0000000000000246 x4 : 0000000000015cff x3 : 0000000000394500 x2 : ffff000682e35e40 x1 : 0000000000364940 x0 : 000000000000001a Call trace: submit_bio_noacct+0x14c/0x4c8 verity_map+0x178/0x2c8 __map_bio+0x228/0x250 dm_submit_bio+0x1c4/0x678 __submit_bio+0x170/0x230 submit_bio_noacct_nocheck+0x16c/0x388 submit_bio_noacct+0x16c/0x4c8 submit_bio+0xb4/0x210 f2fs_submit_read_bio+0x4c/0xf0 f2fs_mpage_readpages+0x3b0/0x5f0 f2fs_readahead+0x90/0xe8 Tighten blk_throtl_activated() to also require that the throttle policy bit is set on the queue: return q->td !=3D NULL && test_bit(blkcg_policy_throtl.plid, q->blkcg_pols); This prevents blk_should_throtl() from accessing throttle group state until policy data has been attached to blkgs. Fixes: a3166c51702b ("blk-throttle: delay initialization until configuratio= n") Co-developed-by: Liang Jie Signed-off-by: Liang Jie Signed-off-by: Han Guangjiang Reviewed-by: Yu Kuai Signed-off-by: Jens Axboe Signed-off-by: Robert Garcia --- block/blk-cgroup.c | 6 ------ block/blk-cgroup.h | 6 ++++++ block/blk-throttle.c | 6 +----- block/blk-throttle.h | 18 +++++++++++------- 4 files changed, 18 insertions(+), 18 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 5a5525d10a5e..3f7cb9d891aa 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -110,12 +110,6 @@ static struct cgroup_subsys_state *blkcg_css(void) return task_css(current, io_cgrp_id); } =20 -static bool blkcg_policy_enabled(struct request_queue *q, - const struct blkcg_policy *pol) -{ - return pol && test_bit(pol->plid, q->blkcg_pols); -} - static void blkg_free_workfn(struct work_struct *work) { struct blkcg_gq *blkg =3D container_of(work, struct blkcg_gq, diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h index b9e3265c1eb3..112bf11d0fad 100644 --- a/block/blk-cgroup.h +++ b/block/blk-cgroup.h @@ -455,6 +455,12 @@ static inline bool blk_cgroup_mergeable(struct request= *rq, struct bio *bio) bio_issue_as_root_blkg(rq->bio) =3D=3D bio_issue_as_root_blkg(bio); } =20 +static inline bool blkcg_policy_enabled(struct request_queue *q, + const struct blkcg_policy *pol) +{ + return pol && test_bit(pol->plid, q->blkcg_pols); +} + void blk_cgroup_bio_start(struct bio *bio); void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta); #else /* CONFIG_BLK_CGROUP */ diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 4aa66c07d2e8..bdf363868ac0 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -1209,17 +1209,13 @@ static int blk_throtl_init(struct gendisk *disk) INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn); throtl_service_queue_init(&td->service_queue); =20 - /* - * Freeze queue before activating policy, to synchronize with IO path, - * which is protected by 'q_usage_counter'. - */ blk_mq_freeze_queue(disk->queue); blk_mq_quiesce_queue(disk->queue); =20 q->td =3D td; td->queue =3D q; =20 - /* activate policy */ + /* activate policy, blk_throtl_activated() will return true */ ret =3D blkcg_activate_policy(disk, &blkcg_policy_throtl); if (ret) { q->td =3D NULL; diff --git a/block/blk-throttle.h b/block/blk-throttle.h index 1a36d1278eea..e1b5343cd43f 100644 --- a/block/blk-throttle.h +++ b/block/blk-throttle.h @@ -154,7 +154,13 @@ void blk_throtl_cancel_bios(struct gendisk *disk); =20 static inline bool blk_throtl_activated(struct request_queue *q) { - return q->td !=3D NULL; + /* + * q->td guarantees that the blk-throttle module is already loaded, + * and the plid of blk-throttle is assigned. + * blkcg_policy_enabled() guarantees that the policy is activated + * in the request_queue. + */ + return q->td !=3D NULL && blkcg_policy_enabled(q, &blkcg_policy_throtl); } =20 static inline bool blk_should_throtl(struct bio *bio) @@ -162,11 +168,6 @@ static inline bool blk_should_throtl(struct bio *bio) struct throtl_grp *tg; int rw =3D bio_data_dir(bio); =20 - /* - * This is called under bio_queue_enter(), and it's synchronized with - * the activation of blk-throtl, which is protected by - * blk_mq_freeze_queue(). - */ if (!blk_throtl_activated(bio->bi_bdev->bd_queue)) return false; =20 @@ -192,7 +193,10 @@ static inline bool blk_should_throtl(struct bio *bio) =20 static inline bool blk_throtl_bio(struct bio *bio) { - + /* + * block throttling takes effect if the policy is activated + * in the bio's request_queue. + */ if (!blk_should_throtl(bio)) return false; =20 --=20 2.34.1