On 4/24/25 8:51 PM, Ming Lei wrote:
> scheduler's ->exit() is called with queue frozen and elevator lock is held, and
> wbt_enable_default() can't be called with queue frozen, otherwise the
> following lockdep warning is triggered:
>
> #6 (&q->rq_qos_mutex){+.+.}-{4:4}:
> #5 (&eq->sysfs_lock){+.+.}-{4:4}:
> #4 (&q->elevator_lock){+.+.}-{4:4}:
> #3 (&q->q_usage_counter(io)#3){++++}-{0:0}:
> #2 (fs_reclaim){+.+.}-{0:0}:
> #1 (&sb->s_type->i_mutex_key#3){+.+.}-{4:4}:
> #0 (&q->debugfs_mutex){+.+.}-{4:4}:
>
> Fix the issue by moving wbt_enable_default() out of bfq's exit(), and
> call it from elevator_change_done().
>
> Meantime add disk->rqos_state_mutex for covering wbt state change, which
> matches the purpose more than ->elevator_lock.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
Looks good to me:
Reviewed-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
