[PATCH] drm/i915: Allow NULL memory region

[Cavitt, Jonathan]

-----Original Message-----
From: Nirmoy Das <nirmoy.das at linux.intel.com> 
Sent: Wednesday, July 17, 2024 8:06 AM
To: Cavitt, Jonathan <jonathan.cavitt at intel.com>; intel-gfx at lists.freedesktop.org
Cc: Gupta, saurabhg <saurabhg.gupta at intel.com>; dan.carpenter at linaro.org; chris.p.wilson at linux.intel.com; Andi Shyti <andi.shyti at linux.intel.com>
Subject: Re: [PATCH] drm/i915: Allow NULL memory region
> 
> 
> On 7/12/2024 11:41 PM, Jonathan Cavitt wrote:
> > Prevent a NULL pointer access in intel_memory_regions_hw_probe.
> >
> > Fixes: 05da7d9f717b ("drm/i915/gem: Downgrade stolen lmem setup warning")
> > Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
> > Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
> > ---
> >   drivers/gpu/drm/i915/intel_memory_region.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_memory_region.c b/drivers/gpu/drm/i915/intel_memory_region.c
> > index 172dfa7c3588b..d40ee1b42110a 100644
> > --- a/drivers/gpu/drm/i915/intel_memory_region.c
> > +++ b/drivers/gpu/drm/i915/intel_memory_region.c
> > @@ -368,8 +368,10 @@ int intel_memory_regions_hw_probe(struct drm_i915_private *i915)
> >   			goto out_cleanup;
> >   		}
> >   
> > -		mem->id = i;
> > -		i915->mm.regions[i] = mem;
> 
> There is a check for mem just before that. You could use 
> IS_ERR_OR_NULL(mem) instead of IS_ERR().

I think you're referring to the "goto out_cleanup" path?

mem being NULL is a valid use case, so we
shouldn't take the error path when it's observed.
-Jonathan Cavitt

> 
> 
> Regards,
> 
> Nirmoy
> 
> > +		if (mem) { /* Skip on non-fatal errors */
> > +			mem->id = i;
> > +			i915->mm.regions[i] = mem;
> > +		}
> >   	}
> >   
> >   	for (i = 0; i < ARRAY_SIZE(i915->mm.regions); i++) {
>