From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 EE7FD35CB7A; Wed, 4 Mar 2026 07:38:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772609902; cv=none; b=G0Mn4nVd7Rp1172F93wqzE25c7vHHa+p/+nBBSnHpclsHoKGk0Jmb6OJZCRbbVFJJys3DPhrfRykwIYI2k3H1HQx/2XDmhIZan3oHPuz3wv0dQdX5wzUfU6TNQLJQ/2kEGNIv/29elhwRMT1Oy9QzvZ3B3vgwHGN/ropHnLVdcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772609902; c=relaxed/simple; bh=mfoop8ZFZvTQ70rW8k+bwTmcnWPolUFqyPFaLre1q6E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dk24XrR5up3c2jPZbSm5NthIk5LlPkfsrUc0mb7VgThUJp+uTFXqMYmO3VMINE/11WeG5ka3JEB+8uOlx3OQI9lbVu/WpNUMWy8igLJI/Yk1TtiIWGMDYyZseQH0f41/2m3vjgMhhulo64afnsa2zVHePcxPOgDeyoGKwq7XZbM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B2F7C2BCB1; Wed, 4 Mar 2026 07:38:19 +0000 (UTC) From: Yu Kuai To: Tejun Heo , Josef Bacik , Jens Axboe Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Zheng Qixing , Ming Lei , Nilay Shroff Subject: [PATCH v3 3/7] blk-cgroup: fix race between policy activation and blkg destruction Date: Wed, 4 Mar 2026 15:38:04 +0800 Message-ID: <20260304073809.3438679-4-yukuai@fnnas.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260304073809.3438679-1-yukuai@fnnas.com> References: <20260304073809.3438679-1-yukuai@fnnas.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Zheng Qixing When switching an IO scheduler on a block device, blkcg_activate_policy() allocates blkg_policy_data (pd) for all blkgs attached to the queue. However, blkcg_activate_policy() may race with concurrent blkcg deletion, leading to use-after-free and memory leak issues. The use-after-free occurs in the following race: T1 (blkcg_activate_policy): - Successfully allocates pd for blkg1 (loop0->queue, blkcgA) - Fails to allocate pd for blkg2 (loop0->queue, blkcgB) - Enters the enomem rollback path to release blkg1 resources T2 (blkcg deletion): - blkcgA is deleted concurrently - blkg1 is freed via blkg_free_workfn() - blkg1->pd is freed T1 (continued): - Rollback path accesses blkg1->pd->online after pd is freed - Triggers use-after-free In addition, blkg_free_workfn() frees pd before removing the blkg from q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd for a blkg that is being destroyed, leaving the newly allocated pd unreachable when the blkg is finally freed. Fix these races by extending blkcg_mutex coverage to serialize blkcg_activate_policy() rollback and blkg destruction, ensuring pd lifecycle is synchronized with blkg list visibility. Link: https://lore.kernel.org/all/20260108014416.3656493-3-zhengqixing@huaweicloud.com/ Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()") Signed-off-by: Zheng Qixing Signed-off-by: Yu Kuai --- block/blk-cgroup.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 0bc7b19399b6..a6ac6ba9430d 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1599,6 +1599,8 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol) if (queue_is_mq(q)) memflags = blk_mq_freeze_queue(q); + + mutex_lock(&q->blkcg_mutex); retry: spin_lock_irq(&q->queue_lock); @@ -1661,6 +1663,7 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol) spin_unlock_irq(&q->queue_lock); out: + mutex_unlock(&q->blkcg_mutex); if (queue_is_mq(q)) blk_mq_unfreeze_queue(q, memflags); if (pinned_blkg) -- 2.51.0