在 2022/02/24 10:15, Ming Lei 写道:
Hi, Ming
If blk_mq_quiesce_queue() is called from __blk_mq_update_nr_hw_queues()
first, and then swithing elevator to none won't trigger the problem.
However, what if blk_mq_unquiesce_queue() from switching elevator
decrease quiesce_depth to 0 first, and then blk_mq_quiesce_queue() is
called from __blk_mq_update_nr_hw_queues(), it seems to me such
concurrent scenarios still exist.
No, the scenario won't exist, once blk_mq_quiesce_queue() returns, it is
guaranteed that:
- in-progress run queue is drained
- no new run queue can be started
I understand that... What I mean about the concurrent scenario is that
reading queue_hw_ctx in blk_mq_run_hw_queues(), not the actual run
queue blk_mq_run_hw_queue():
t1 t2
elevator_switch
blk_mq_quiesce_queue -> quiesce_depth = 1
blk_mq_unquiesce_queue-> quiesce_depth = 0
blk_mq_run_hw_queues
__blk_mq_update_nr_hw_queues
blk_mq_quiesce_queue
queue_for_each_hw_ctx
-> quiesce_queue can't prevent reading queue_hw_ctx
blk_mq_run_hw_queue
//need_run is always false, nothing to do
Am I missing something about blk_mq_quiesce_queue ?
Thanks,
Kuai
