Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied

Andy Shevchenko
2020-03-26T14:23:53Z

On Thu, Mar 26, 2020 at 01:45:50PM +0000, Grant Likely wrote:
> On 26/03/2020 12:03, Andy Shevchenko wrote:
> > On Thu, Mar 26, 2020 at 11:45:18AM +0200, Peter Ujfalusi wrote:
> > > On 26/03/2020 10.39, Rafael J. Wysocki wrote:
> > > > On Wed, Mar 25, 2020 at 11:09 PM Saravana Kannan <saravanak@google.com> wrote:
> > > > > On Wed, Mar 25, 2020 at 5:51 AM Andy Shevchenko
> > > > > <andriy.shevchenko@linux.intel.com> wrote:
> >
> > ...
> >
> > > > OK, so the situation right now is that commit 58b116bce136 has
> > > > introduced a regression and so it needs to be fixed or reverted. The
> > > > cases that were previously broken and were unbroken by that commit
> > > > don't matter here, so you cannot argue that they would be "broken".
> > >
> > > commit 58b116bce136 is from 2014 and the whole ULPI support for dwc3
> > > came in a year later.
> > > While I agree that 58b116bce136 fail to handle came a year later, but
> > > technically it did not introduced a regression.
> > >
> > > The revert on the other hand is going to introduce a regression as
> > > things were working fine since 2014. Not sure why the dwc3 issue got
> > > this long to be noticed as the 58b116bce136 was already in kernel when
> > > the ULPI support was added...
> >
> > I dare to say that is luck based on people's laziness to figure out the root
> > cause. As I pointed out in email to Saravana the issue is not limited to USB
> > case and, if my memory doesn't trick me out, I suffered from it approximately
> > in ~2014-2015 with pin control tables.
>
> I've not been involved in this for a very long time, but from our past
> conversations and the description that is given here I still feel that this
> problem is a design bug on the dwc3 driver dependencies rather than a
> failure with driver core. dwc3 is doing something rather convoluted and it
> would be worth reevaluating how probe failures are unwound on that
> particular driver stack.

I disagree. Have you chance to look into another example I gave to Saravana?

The unbalanced increment is fragile per se, because you can't guarantee that
it will be no unsynchronization between probed successfully (unrelated!) and
deferred drivers.

--
With Best Regards,
Andy Shevchenko