[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 8:22 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 7/17/2024 5:11 PM, Cavitt, Jonathan wrote:
> > -----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?
> 
> Yes.
> 
> >
> > mem being NULL is a valid use case, so we
> > shouldn't take the error path when it's observed.
> Not an error path if you return expected/correct value.

intel_memory_regions_driver_release releases all previously
grabbed memory regions in the out_cleanup path.
-Jonathan Cavitt

> 
> You could do
> diff --git a/drivers/gpu/drm/i915/intel_memory_region.c b/drivers/gpu/drm/i915/intel_memory_region.c
> index 172dfa7c3588..41ef7fdfa69b 100644
> --- a/drivers/gpu/drm/i915/intel_memory_region.c
> +++ b/drivers/gpu/drm/i915/intel_memory_region.c
> @@ -362,9 +362,10 @@ int intel_memory_regions_hw_probe(struct drm_i915_private *i915)
> 
>                  if (IS_ERR(mem)) {
>                          err = PTR_ERR(mem);
> -                       drm_err(&i915->drm,
> -                               "Failed to setup region(%d) type=%d\n",
> -                               err, type);
> +                       if (err)
> +                               drm_err(&i915->drm,
> +                                       "Failed to setup region(%d) type=%d\n",
> +                                       err, type);
>                          goto out_cleanup;
>                  }
> 
> PTR_ERR(NULL) should be 0 I think and could even add a info saying skipping setting up that reason.
> 
> Regards,
> Nirmoy
> 
> > -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++) {
>