From 2d8951aee844b7c6d146e25b5c3eebc1c72aa6ff Mon Sep 17 00:00:00 2001 From: Nilay Shroff Date: Mon, 12 May 2025 14:43:38 +0530 Subject: [PATCH] block: unfreeze queue if realloc tag set fails during nr_hw_queues update MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit In __blk_mq_update_nr_hw_queues(), the current sequence involves: 1. unregistering sysfs/debugfs attributes 2. freeze the queue 3. reallocating the tag set 4. updating the queue map 5. reallocating hardware contexts 6. updating the elevator (which unfreeze the queue again) 7. re-register sysfs/debugfs attributes If tag set reallocation fails at step 3, the function skips steps 4–6 and proceeds directly to step 7, re-registering the sysfs/debugfs attributes without unfreezing the queue first. This is incorrect and can lead to a system hang or lockdep splat, as the queue remains frozen and is never properly unfrozen. This patch addresses the issue by explicitly unfreezing the queue before re-registering the sysfs/debugfs attributes in the event of a tag set reallocation failure. Fixes: 9dc7a882ce96 ("block: move hctx debugfs/sysfs registering out of freezing queue") Signed-off-by: Nilay Shroff Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/20250512092952.135887-1-nilay@linux.ibm.com Signed-off-by: Jens Axboe --- block/blk-mq.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 4f79a9808fd1..cbc9a9f97a31 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -5002,8 +5002,11 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_freeze_queue_nomemsave(q); - if (blk_mq_realloc_tag_set_tags(set, nr_hw_queues) < 0) + if (blk_mq_realloc_tag_set_tags(set, nr_hw_queues) < 0) { + list_for_each_entry(q, &set->tag_list, tag_set_list) + blk_mq_unfreeze_queue_nomemrestore(q); goto reregister; + } fallback: blk_mq_update_queue_map(set); -- 2.25.1