Re: [PATCH 0/4] blk-mq: support to use hw tag for scheduling

On Thu, 2017-05-04 at 01:19 +0800, Ming Lei wrote:

On Wed, May 03, 2017 at 05:08:30PM +0000, Bart Van Assche wrote:

quoted

Callers of blk_mq_quiesce_queue() really need blk_mq_stop_hw_queue() to
cancel delayed work synchronously. The above call stack shows that we h=

ave

quoted

to do something about the blk_mq_stop_hw_queue() calls from inside .que=

ue_rq()

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functions for queues for which BLK_MQ_F_BLOCKING has not been set. I'm =

not

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sure what the best approach would be: setting BLK_MQ_F_BLOCKING for que=

ues

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that call blk_mq_stop_hw_queue() from inside .queue_rq() or creating tw=

o

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versions of blk_mq_stop_hw_queue().

=20
I think either synchronize_srcu() or synchronize_rcu() can handle=20
this, since they are waiting for completion of .queue_rq(). So looks
cancel_delayed_work_sync() shouldn't be needed?

Hello Ming,

What you wrote is not correct. synchronize_*rcu() only waits for ongoing
.queue_rq() calls. cancel_delayed_work() will return immediately if it is
called after hctx->run_work has already been started. And the hctx->run_wor=
k
handler can trigger new .queue_rq() calls after synchronize_*rcu() has
already returned.

Bart.=