Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock_t.

[Guenter Roeck]

On 11/27/24 08:53, Sebastian Andrzej Siewior wrote:
> On 2024-11-27 08:02:50 [-0800], Guenter Roeck wrote:
> > On 11/27/24 07:39, Andreas Larsson wrote:
> > > Even though this is for sparc64, there is work being done looking into
> > > enabling RT for sparc32. If the amount of fixes needed to keep
> > > PROVE_RAW_LOCK_NESTING enabled is quite small at the moment I'd rather
> > > see it enabled for sparc rather than risking it becoming worse in the
> > > future.
>
> Okay. So you seem to be in favour of fixing the sparc64 splats Guenter
> reported?
>
> > > I don't know what the situation is for other architectures that does not
> > > support RT.
> >
> > For my part I still don't understand why PROVE_RAW_LOCK_NESTING is no longer
> > a configurable option, or in other words why it is mandated even for architectures
> > not supporting RT. To me this means that I'll either have to disable PROVE_LOCKING
> > for sparc or live with endless warning backtraces. The latter obscures real
> > problems, so it is a no-go.
>
> It is documented in Documentation/locking/locktypes.rst how the locks
> should nest. It is just nobody enabled it on sparc64 and tested. The
> option was meant temporary until the big read blocks are cleared.

That doesn't explain why PROVE_RAW_LOCK_NESTING is now mandatory if
PROVE_LOCKING is enabled, even on architectures where is was not tested.
I am all for testing, but that doesn't include making it mandatory
even where it is known to fail. Enabling it by default, sure, no problem.
Dropping the option entirely after it is proven to no longer needed,
also no problem. But force-enabling it even where untested or, worse,
known to fail, is two steps too far.

> > So, if people want to keep mandating PROVE_RAW_LOCK_NESTING together with
> > PROVE_LOCKING for all architectures, I'll disable PROVE_LOCKING for sparc
> > in my testing. NP, just let me know. I'll then do the same for other
> > architectures not supporting RT if I hit the same problem there.
>
> Waiman posted a patch to disable it on architectures that don't support
> PREEMPT_RT. You could also post the patches you discussed. Andreas does
> not seem to be against it (but then I don't know if he is a 32 or 64bit
> guy). I did not year from other architectures so far.

I don't have time to work through all the issues, much less to argue with
affected maintainers to get the various patches accepted. I am open to fixing
regressions if I can, but it appears that this is not considered to be a
regression. I'll just disable PROVE_LOCKING for affected architectures
in my testing after -rc1 is out.

Thanks,
Guenter