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From: Ming Lei <ming.lei@redhat.com>
To: Yu Kuai <yukuai@fnnas.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org, tj@kernel.org,
	nilay@linux.ibm.com
Subject: Re: [PATCH v7 09/16] blk-throttle: fix possible deadlock for fs reclaim under rq_qos_mutex
Date: Wed, 7 Jan 2026 20:04:43 +0800	[thread overview]
Message-ID: <aV5L25KZkM4dvzLD@fedora> (raw)
In-Reply-To: <20251231085126.205310-10-yukuai@fnnas.com>

On Wed, Dec 31, 2025 at 04:51:19PM +0800, Yu Kuai wrote:
> blk_throtl_init() can be called with rq_qos_mutex held from blkcg
> configuration, and fs reclaim can be triggered because GFP_KERNEL is used
> to allocate memory. This can deadlock because rq_qos_mutex can be held
> with queue frozen.
> 
> Fix the problem by using blkg_conf_open_bdev_frozen(), also remove
> useless queue frozen from blk_throtl_init().
> 
> Signed-off-by: Yu Kuai <yukuai@fnnas.com>
> ---

I think this patch goes toward wrong direction by enlarging queue freeze
scope, and blkg_conf_prep() may run into percpu allocation, then new
lockdep warning could be triggered.

IMO, we should try to reduce blkg_conf_open_bdev_frozen() uses, instead of
adding more.

Thanks,
Ming


  parent reply	other threads:[~2026-01-07 12:05 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-12-31  8:51 [PATCH v7 00/16] blk-mq: fix possible deadlocks Yu Kuai
2025-12-31  8:51 ` [PATCH v7 01/16] blk-wbt: factor out a helper wbt_set_lat() Yu Kuai
2025-12-31  8:51 ` [PATCH v7 02/16] blk-wbt: fix possible deadlock to nest pcpu_alloc_mutex under q_usage_counter Yu Kuai
2026-01-07  9:30   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 03/16] blk-mq-debugfs: factor out a helper to register debugfs for all rq_qos Yu Kuai
2025-12-31  8:51 ` [PATCH v7 04/16] blk-rq-qos: fix possible debugfs_mutex deadlock Yu Kuai
2026-01-07  9:41   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 05/16] blk-mq-debugfs: make blk_mq_debugfs_register_rqos() static Yu Kuai
2026-01-07  9:42   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 06/16] blk-mq-debugfs: remove blk_mq_debugfs_unregister_rqos() Yu Kuai
2026-01-04 16:37   ` Nilay Shroff
2026-01-07  9:48   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 07/16] blk-mq-debugfs: add missing debugfs_mutex in blk_mq_debugfs_register_hctxs() Yu Kuai
2026-01-04 16:37   ` Nilay Shroff
2026-01-07  9:51   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 08/16] blk-mq-debugfs: warn about possible deadlock Yu Kuai
2026-01-04 16:38   ` Nilay Shroff
2026-01-07  9:56   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 09/16] blk-throttle: fix possible deadlock for fs reclaim under rq_qos_mutex Yu Kuai
2026-01-04 16:38   ` Nilay Shroff
2026-01-07 12:04   ` Ming Lei [this message]
2026-01-08 16:56     ` Yu Kuai
2026-01-09  2:18       ` Ming Lei
2026-01-09  2:22         ` Yu Kuai
2026-01-09  2:26           ` Ming Lei
2026-01-09  9:09       ` Nilay Shroff
2026-02-11  2:07         ` Yu Kuai
2025-12-31  8:51 ` [PATCH v7 10/16] block/blk-rq-qos: add a new helper rq_qos_add_frozen() Yu Kuai
2026-01-04 16:39   ` Nilay Shroff
2026-01-07 12:14   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 11/16] blk-wbt: fix incorrect lock order for rq_qos_mutex and freeze queue Yu Kuai
2026-01-04 16:39   ` Nilay Shroff
2026-01-07 12:14   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 12/16] blk-iocost: " Yu Kuai
2026-01-04 16:39   ` Nilay Shroff
2026-01-07 12:17   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 13/16] blk-iolatency: " Yu Kuai
2026-01-04 16:40   ` Nilay Shroff
2026-01-07 12:20   ` Ming Lei
2025-12-31  8:51 ` [PATCH v7 14/16] block/blk-rq-qos: cleanup rq_qos_add() Yu Kuai
2026-01-04 16:40   ` Nilay Shroff
2025-12-31  8:51 ` [PATCH v7 15/16] blk-rq-qos: remove queue frozen from rq_qos_del() Yu Kuai
2026-01-04 16:40   ` Nilay Shroff
2025-12-31  8:51 ` [PATCH v7 16/16] blk-cgroup: remove queue frozen from blkcg_activate_policy() Yu Kuai
2026-01-04 16:41   ` Nilay Shroff

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