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block: protect wbt_lat_usec using q->elevator_lock

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The wbt latency and state could be updated while initializing the
elevator or exiting the elevator. It could be also updated while
configuring IO latency QoS parameters using cgroup. The elevator
code path is now protected with q->elevator_lock. So we should
protect the access to sysfs attribute wbt_lat_usec using q->elevator
_lock instead of q->sysfs_lock. White we're at it, also protect
ioc_qos_write(), which configures wbt parameters via cgroup, using
q->elevator_lock.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304102551.2533767-7-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nilay Shroff
2025-03-04 15:52:35 +05:30
committed by Jens Axboe
parent 3efe7571c3
commit 245618f8e4
3 changed files with 12 additions and 14 deletions
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4
include/linux/blkdev.h
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@@ -563,8 +563,8 @@ struct request_queue {
/*
* Protects against I/O scheduler switching, particularly when
* updating q->elevator. Since the elevator update code path may
* also modify q->nr_requests, this lock also protects the sysfs
* attribute nr_requests.
* also modify q->nr_requests and wbt latency, this lock also
* protects the sysfs attributes nr_requests and wbt_lat_usec.
* To ensure proper locking order during an elevator update, first
* freeze the queue, then acquire ->elevator_lock.
*/