On Fri, 2018-08-10 at 09:51 +0800, jianchao.wang wrote:
> On 08/10/2018 03:41 AM, Bart Van Assche wrote:
> > +
> > +   blk_set_pm_only(q);
> > +   /*
> > +    * This function only gets called if the most recent
> > +    * pm_request_resume() call occurred at least autosuspend_delay_ms
> > +    * ago. Since blk_queue_enter() is called by the request allocation
> > +    * code before pm_request_resume(), if no requests have a tag assigned
> > +    * it is safe to suspend the device.
> > +    */
> > +   ret = -EBUSY;
> > +   if (blk_requests_in_flight(q) == 0) {
> > +           /*
> > +            * Call synchronize_rcu() such that later blk_queue_enter()
> > +            * calls see the preempt-only state. See also
> > +            * 
> > https://urldefense.proofpoint.com/v2/url?u=http-3A__lwn.net_Articles_573497_&d=DwIBAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26ATvfo6QSTvZyQ&m=U9uPCJD2WnkXvdzrWaKPh2wJuk8-IHvxZ9sWDVrg2Tg&s=c9E23TPCpNQkiZpuzGztwHxjWF8qrESfRnPmI-e-Z48&e=
> > .
> > +            */
> > +           synchronize_rcu();
> > +           if (blk_requests_in_flight(q) == 0)
> > +                   ret = 0;
> > +   }
> 
> I still think blk_set_pm_only should be moved after blk_requests_in_flight.
> Otherwise, the normal IO will be blocked for a little while if there are still
> busy requests.

Hi Jianchao,

Although I think it is unlikely that the scenario you described will happen, I
will make the change you requested.

Bart.

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