Re: [PATCH V7 1/9] blk-mq: grab .q_usage_counter when queuing request from plug code path

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On Thu, Apr 25, 2019 at 07:32:34AM +0200, Christoph Hellwig wrote:
> On Thu, Apr 25, 2019 at 08:53:34AM +0800, Ming Lei wrote:
> > It isn't in other callers of blk_mq_sched_insert_requests(), it is just
> > needed in some corner case like flush plug context.
> > 
> > For other callers of blk_mq_sched_insert_requests(), it is guaranteed
> > that request queue's ref is held.
> 
> In both Linus' tree and Jens' for-5.2 tree I only see these two
> callers of blk_mq_sched_insert_requests.  What am I missing?

OK, what I meant is that the issue is flush plug context specific.
And I didn't notice that this function is only called by
blk_mq_flush_plug_list().

Then it is fine to move the percpu_ref_get()/percpu_ref_put() into
the function, better with comment on this issue.

Thanks, 
Ming



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