[PATCH 1/1] drm/amdgpu: ignore -EPERM error from debugfs

[Das, Nirmoy]

On 10/5/2021 3:22 PM, Christian König wrote:
>
>
> Am 05.10.21 um 15:11 schrieb Nirmoy Das:
>> Debugfs core APIs will throw -EPERM when user disables debugfs
>> using CONFIG_DEBUG_FS_ALLOW_NONE or with kernel param. We shouldn't
>> see that as an error. Also validate drm root dentry before creating
>> amdgpu debugfs files.
>>
>> Signed-off-by: Nirmoy Das <nirmoy.das at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> index 6611b3c7c149..d786072e918b 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>> @@ -1617,6 +1617,16 @@ int amdgpu_debugfs_init(struct amdgpu_device 
>> *adev)
>>       struct dentry *ent;
>>       int r, i;
>>   +    if (IS_ERR(root)) {
>> +        /* When debugfs is disabled we get -EPERM which is not an
>> +         * error as this is user controllable.
>> +         */
>
> Well setting primary->debugfs_root to an error code is probably not a 
> good idea to begin with.
>
> When debugfs is disabled that should most likely be NULL.


If we set primary->debugfs_root to  NULL then we need to add bunch of 
NULL checks everywhere before creating any debugfs files

because debugfs_create_{file|dir}() with NULL root is still valid.  I am 
assuming a hypothetical case when debugfs_root dir creation fails  even 
with debugfs enabled

but further calls are successful.  This wont be a problem if we 
propagate the error code.


Regards,

Nirmoy

>
> Regards,
> Christian.
>
>> +        if (PTR_ERR(root) == -EPERM)
>> +            return 0;
>> +
>> +        return PTR_ERR(ent);
>> +    }
>> +
>>       ent = debugfs_create_file("amdgpu_preempt_ib", 0600, root, adev,
>>                     &fops_ib_preempt);
>>       if (IS_ERR(ent)) {
>