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block: use trylock to avoid lockdep circular dependency in sysfs

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Use trylock instead of blocking lock acquisition for update_nr_hwq_lock
in queue_requests_store() and elv_iosched_store() to avoid circular lock
dependency with kernfs active reference during concurrent disk deletion:

  update_nr_hwq_lock -> kn->active (via del_gendisk -> kobject_del)
  kn->active -> update_nr_hwq_lock (via sysfs write path)

Return -EBUSY when the lock is not immediately available.

Reported-and-tested-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/linux-block/CAHj4cs-em-4acsHabMdT=jJhXkCzjnprD-aQH1OgrZo4nTnmMw@mail.gmail.com/
Fixes: 626ff4f8eb ("blk-mq: convert to serialize updating nr_requests with update_nr_hwq_lock")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2026-03-05 11:15:50 +08:00 • committed by Jens Axboe
parent d90c470b0e
commit ce8ee8583e
2 changed files with 18 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

8
block/blk-sysfs.c
View file

@ -78,8 +78,14 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count)
/*
* Serialize updating nr_requests with concurrent queue_requests_store()
* and switching elevator.
*
* Use trylock to avoid circular lock dependency with kernfs active
* reference during concurrent disk deletion:
* update_nr_hwq_lock -> kn->active (via del_gendisk -> kobject_del)
* kn->active -> update_nr_hwq_lock (via this sysfs write path)
*/
down_write(&set->update_nr_hwq_lock);
if (!down_write_trylock(&set->update_nr_hwq_lock))
return -EBUSY;
if (nr == q->nr_requests)
goto unlock;

12
block/elevator.c
View file

@ -807,7 +807,16 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
elv_iosched_load_module(ctx.name);
ctx.type = elevator_find_get(ctx.name);
down_read(&set->update_nr_hwq_lock);
/*
* Use trylock to avoid circular lock dependency with kernfs active
* reference during concurrent disk deletion:
* update_nr_hwq_lock -> kn->active (via del_gendisk -> kobject_del)
* kn->active -> update_nr_hwq_lock (via this sysfs write path)
*/
if (!down_read_trylock(&set->update_nr_hwq_lock)) {
ret = -EBUSY;
goto out;
}
if (!blk_queue_no_elv_switch(q)) {
ret = elevator_change(q, &ctx);
if (!ret)
@ -817,6 +826,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
}
up_read(&set->update_nr_hwq_lock);
out:
if (ctx.type)
elevator_put(ctx.type);
return ret;