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blk-rq-qos: fix possible debugfs_mutex deadlock

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Currently rq-qos debugfs entries are created from rq_qos_add(), while
rq_qos_add() can be called while queue is still frozen. This can
deadlock because creating new entries can trigger fs reclaim.

Fix this problem by delaying creating rq-qos debugfs entries after queue
is unfrozen.

- For wbt, 1) it can be initialized by default, fix it by calling new
  helper after wbt_init() from wbt_init_enable_default(); 2) it can be
  initialized by sysfs, fix it by calling new helper after queue is
  unfrozen from wbt_set_lat().
- For iocost and iolatency, they can only be initialized by blkcg
  configuration, however, they don't have debugfs entries for now, hence
  they are not handled yet.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai
2026-02-02 16:05:19 +08:00
committed by Jens Axboe
parent 3f0bea9f3b
commit 3c17a346ff
2 changed files with 12 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
block/blk-rq-qos.c
View File

@@ -347,13 +347,6 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q);
blk_mq_unfreeze_queue(q, memflags);
if (rqos->ops->debugfs_attrs) {
mutex_lock(&q->debugfs_mutex);
blk_mq_debugfs_register_rqos(rqos);
mutex_unlock(&q->debugfs_mutex);
}
return 0;
ebusy:
blk_mq_unfreeze_queue(q, memflags);

13
block/blk-wbt.c
View File

@@ -774,6 +774,7 @@ EXPORT_SYMBOL_GPL(wbt_enable_default);
void wbt_init_enable_default(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
struct rq_wb *rwb;
if (!__wbt_enable_default(disk))
@@ -783,8 +784,14 @@ void wbt_init_enable_default(struct gendisk *disk)
if (WARN_ON_ONCE(!rwb))
return;
if (WARN_ON_ONCE(wbt_init(disk, rwb)))
if (WARN_ON_ONCE(wbt_init(disk, rwb))) {
wbt_free(rwb);
return;
}
mutex_lock(&q->debugfs_mutex);
blk_mq_debugfs_register_rq_qos(q);
mutex_unlock(&q->debugfs_mutex);
}
static u64 wbt_default_latency_nsec(struct request_queue *q)
@@ -1008,5 +1015,9 @@ int wbt_set_lat(struct gendisk *disk, s64 val)
blk_mq_unquiesce_queue(q);
out:
blk_mq_unfreeze_queue(q, memflags);
mutex_lock(&q->debugfs_mutex);
blk_mq_debugfs_register_rq_qos(q);
mutex_unlock(&q->debugfs_mutex);
return ret;
}