On Mon, 2015-09-07 at 10:48 -0400, Alan Stern wrote:
> On Mon, 7 Sep 2015, Xue, Ken wrote:
>
> > Hi Alan and James,
> > I found a bug about sr device runtime suspend & resume which is introduced by your patch about fixing NULL pointer dereference in runtime PM.
> > You know that sr device only has runtime suspend routine but doesn't have resume routine.
> > After your patch, blk_ *_ runtime_suspend will be called when runtime suspend. But blk_ *_ runtime_resume cannot be called when resume.
> > So, sr device cannot work correctly after 1st runtime suspend.
>
> Argh. Things just get more and more complicated...
>
> > I want to make a dummy runtime resume routine in sr.c for fixing this runtime issue of sr device.
> > If you guys think a dummy runtime routine for resume is acceptable, I can submit patch later.
>
> A dummy routine isn't the greatest solution. Eventually someone will
> see it, wonder why it's there, and remove it.
>
> The real issue we need to address here is whether the driver has asked
> for request-queue-oriented runtime PM by calling blk_pm_runtime_init().
> If it hasn't then we need to skip at least the calls to
> blk_{pre|post}_runtime_{suspend|resume}.
>
> The patch I wrote uses the existence of runtime-PM callbacks as an
> indicator for this, but evidently it isn't adequate. A more direct
> approach would be to test whether sdev->request_queue->dev is non-NULL,
> but this would be a layering violation.
>
> Should we add a SCSI-level flag to indicate that blk_pm_runtime_init()
> has been called?
Can we check whether sdev->request_queue->dev is non-NULL in blk_{pre|
post}_runtime_{suspend|resume}?
just use simple codes like:
int blk_pre_runtime_suspend(struct request_queue *q)
{
...
if(!q->dev)
return -ENODEV;
..
}
>
> Alan Stern
>
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