[PATCH] drm/i915: Allow NULL memory region

[Nirmoy Das]

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.

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++) {