kernel/linux.git/block/blk-mq-debugfs.c, branch v7.0.10

blk-mq: use NOIO context to prevent deadlock during debugfs creation

2026-02-16T17:47:25+00:00

Creating debugfs entries can trigger fs reclaim, which can enter back into the block layer request_queue. This can cause deadlock if the queue is frozen. Previously, a WARN_ON_ONCE check was used in debugfs_create_files() to detect this condition, but it was racy since the queue can be frozen from another context at any time. Introduce blk_debugfs_lock()/blk_debugfs_unlock() helpers that combine the debugfs_mutex with memalloc_noio_save()/restore() to prevent fs reclaim from triggering block I/O. Also add blk_debugfs_lock_nomemsave() and blk_debugfs_unlock_nomemrestore() variants for callers that don't need NOIO protection (e.g., debugfs removal or read-only operations). Replace all raw debugfs_mutex lock/unlock pairs with these helpers, using the _nomemsave/_nomemrestore variants where appropriate. Reported-by: Yi Zhang Closes: https://lore.kernel.org/all/CAHj4cs9gNKEYAPagD9JADfO5UH+OiCr4P7OO2wjpfOYeM-RV=A@mail.gmail.com/ Reported-by: Shinichiro Kawasaki Closes: https://lore.kernel.org/all/aYWQR7CtYdk3K39g@shinmob/ Suggested-by: Christoph Hellwig Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe

blk-mq-debugfs: warn about possible deadlock

2026-02-02T14:05:19+00:00

Creating new debugfs entries can trigger fs reclaim, hence we can't do this with queue frozen, meanwhile, other locks that can be held while queue is frozen should not be held as well. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

blk-mq-debugfs: add missing debugfs_mutex in blk_mq_debugfs_register_hctxs()

2026-02-02T14:05:19+00:00

In blk_mq_update_nr_hw_queues(), debugfs_mutex is not held while creating debugfs entries for hctxs. Hence add debugfs_mutex there, it's safe because queue is not frozen. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

blk-mq-debugfs: remove blk_mq_debugfs_unregister_rqos()

2026-02-02T14:05:19+00:00

Because this helper is only used by iocost and iolatency, while they don't have debugfs entries. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

blk-mq-debugfs: make blk_mq_debugfs_register_rqos() static

2026-02-02T14:05:19+00:00

Because it's only used inside blk-mq-debugfs.c now. Reviewed-by: Nilay Shroff Signed-off-by: Yu Kuai Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

blk-mq-debugfs: factor out a helper to register debugfs for all rq_qos

2026-02-02T14:05:19+00:00

There is already a helper blk_mq_debugfs_register_rqos() to register one rqos, however this helper is called synchronously when the rqos is created with queue frozen. Prepare to fix possible deadlock to create blk-mq debugfs entries while queue is still frozen. Reviewed-by: Ming Lei Reviewed-by: Nilay Shroff Signed-off-by: Yu Kuai Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

blk-mq: add QUEUE_FLAG_BIO_ISSUE_TIME

2025-09-10T11:23:45+00:00

bio->issue_time_ns is initialized for every bio, however, it's only used by blk-iolatency. Add a new queue_flag and only set this flag when blk-iolatency is enabled, so that extra blk_time_get_ns() can be saved for disks that blk-iolatency is not enabled. Signed-off-by: Yu Kuai Signed-off-by: Jens Axboe

block: avoid cpu_hotplug_lock depedency on freeze_lock

2025-08-21T13:11:11+00:00

A recent lockdep[1] splat observed while running blktest block/005 reveals a potential deadlock caused by the cpu_hotplug_lock dependency on ->freeze_lock. This dependency was introduced by commit 033b667a823e ("block: blk-rq-qos: guard rq-qos helpers by static key"). That change added a static key to avoid fetching q->rq_qos when neither blk-wbt nor blk-iolatency is configured. The static key dynamically patches kernel text to a NOP when disabled, eliminating overhead of fetching q->rq_qos in the I/O hot path. However, enabling a static key at runtime requires acquiring both cpu_hotplug_lock and jump_label_mutex. When this happens after the queue has already been frozen (i.e., while holding ->freeze_lock), it creates a locking dependency from cpu_hotplug_lock to ->freeze_lock, which leads to a potential deadlock reported by lockdep [1]. To resolve this, replace the static key mechanism with q->queue_flags: QUEUE_FLAG_QOS_ENABLED. This flag is evaluated in the fast path before accessing q->rq_qos. If the flag is set, we proceed to fetch q->rq_qos; otherwise, the access is skipped. Since q->queue_flags is commonly accessed in IO hotpath and resides in the first cacheline of struct request_queue, checking it imposes minimal overhead while eliminating the deadlock risk. This change avoids the lockdep splat without introducing performance regressions. [1] https://lore.kernel.org/linux-block/4fdm37so3o4xricdgfosgmohn63aa7wj3ua4e5vpihoamwg3ui@fq42f5q5t5ic/ Reported-by: Shinichiro Kawasaki Closes: https://lore.kernel.org/linux-block/4fdm37so3o4xricdgfosgmohn63aa7wj3ua4e5vpihoamwg3ui@fq42f5q5t5ic/ Fixes: 033b667a823e ("block: blk-rq-qos: guard rq-qos helpers by static key") Tested-by: Shin'ichiro Kawasaki Signed-off-by: Nilay Shroff Reviewed-by: Ming Lei Reviewed-by: Yu Kuai Link: https://lore.kernel.org/r/20250814082612.500845-4-nilay@linux.ibm.com Signed-off-by: Jens Axboe

blk-mq-debugfs: use debugfs_get_aux()

2025-07-09T11:30:29+00:00

instead of manually stashing the data pointer into parent directory inode's ->i_private, just pass it to debugfs_create_file_aux() so that it can be extracted without that insane chasing through ->d_parent. Signed-off-by: Al Viro Link: https://lore.kernel.org/r/20250702212818.GJ3406663@ZenIV Signed-off-by: Greg Kroah-Hartman

block: add new helper for disabling elevator switch when deleting disk

2025-05-06T13:43:43+00:00

Add new helper disable_elv_switch() and new flag QUEUE_FLAG_NO_ELV_SWITCH for disabling elevator switch before deleting disk: - originally flag QUEUE_FLAG_REGISTERED is added for preventing elevator switch during removing disk, but this flag has been used widely for other purposes, so add one new flag for disabling elevator switch only - for avoiding deadlock risk, we have to move elevator queue register/unregister out of elevator lock and queue freeze, which will be done in next patch. However, this way adds small race window between elevator switch and deleting ->queue_kobj, in which elevator queue register/unregister could be run concurrently. The added helper will be used for avoiding the race in the following patch. - drain in-progress elevator switch before deleting disk Suggested-by: Nilay Shroff Reviewed-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Signed-off-by: Ming Lei Reviewed-by: Nilay Shroff Link: https://lore.kernel.org/r/20250505141805.2751237-21-ming.lei@redhat.com Signed-off-by: Jens Axboe