On Tue, 8 Sep 2015, Ken Xue wrote:
> 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)
Missing space between "if" and "(". :-)
> return -ENODEV;
Return ret (i.e., 0), not -ENODEV. If, for some reason, a device uses
runtime PM that's not based on the state of the request queue, we don't
want to subvert that other mechanism.
> ..
> }
I agree, this appears to be the best solution. (That, plus reverting
my earlier patch.) I originally avoided putting in this test because
it seemed like unnecessary overhead. Now we see that the overhead is
necessary after all.
Alan Stern
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