Re: [PATCH] blk-mq: put the reference of the io scheduler module after switching back

[Yu Kuai]

Hi,

在 2022/10/13 21:03, Jinlong Chen 写道:
> Sorry for the disturbance.
>
> This patch is just wrong. elevator_switch_mq does not increase the reference
>   count of the io scheduler module to which we are switching. Hence, we do not
>   need to put the reference back manually.

I'm confused here, cause I do think this patch make sense.

blk_mq_update_nr_hw_queues
 // for each queue using the tagset
 blk_mq_freeze_queue
 // if current elevator is not none, swith to none
 blk_mq_elv_switch_none
  // elevator need to be switched back, got a reference to
  // prevent module to be removed.
  __module_get
  elevator_switch(q, NULL);

 // switch back from none elevator
 blk_mq_elv_switch_back
  -> should release the module reference here
 blk_mq_unfreeze_queue

By the way, I do not test yet, but I think problem can be reporduced:

1. modprobe bfq
2. switch elevator to bfq
3. trigger blk_mq_update_nr_hw_queues
4. switch elevator to none
5. rmmod bfq will fail

Thanks,
Kuai
> Sincerely
> Jinlong Chen
> .