Commit b126d9d7 authored May 05, 2025 by Ming Lei Committed by Jens Axboe May 06, 2025

block: don't allow to switch elevator if updating nr_hw_queues is in-progress



Elevator switch code is another `nr_hw_queue` reader in non-fast-IO code
path, so it can't be done if updating `nr_hw_queues` is in-progress.

Take same approach with not allowing add/del disk when updating
nr_hw_queues is in-progress, by grabbing read lock of
set->update_nr_hwq_sema.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/linux-block/aAWv3NPtNIKKvJZc@fedora/

 [1]
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Closes: https://lore.kernel.org/linux-block/mz4t4tlwiqjijw3zvqnjb7ovvvaegkqganegmmlc567tt5xj67@xal5ro544cnc/


Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250505141805.2751237-10-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 98e68f67

block/elevator.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -723,6 +723,7 @@ ssize_t elv_iosched_store(struct gendisk disk, const char buf,
		int ret;
		unsigned int memflags;
		struct request_queue *q = disk->queue;
		struct blk_mq_tag_set *set = q->tag_set;

		/*
		* If the attribute needs to load a module, do it before freezing the
		@@ -734,6 +735,7 @@ ssize_t elv_iosched_store(struct gendisk disk, const char buf,

		elv_iosched_load_module(name);

		down_read(&set->update_nr_hwq_lock);
		memflags = blk_mq_freeze_queue(q);
		mutex_lock(&q->elevator_lock);
		ret = elevator_change(q, name);
		@@ -741,6 +743,7 @@ ssize_t elv_iosched_store(struct gendisk disk, const char buf,
		ret = count;
		mutex_unlock(&q->elevator_lock);
		blk_mq_unfreeze_queue(q, memflags);
		up_read(&set->update_nr_hwq_lock);
		return ret;
		}