Re: [Outreachy kernel] [PATCH] drm/amdgpu: use DEFINE_DEBUGFS_ATTRIBUTE with debugfs_create_file_unsafe()

From: "Christian König" <christian.koenig@amd.com>
To: Deepak R Varma <mh12gx2825@gmail.com>,
	Greg KH <gregkh@linuxfoundation.org>
Cc: David Airlie <airlied@linux.ie>,
	daniel.vetter@ffwll.ch, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, melissa.srw@gmail.com,
	outreachy-kernel@googlegroups.com, amd-gfx@lists.freedesktop.org,
	Daniel Vetter <daniel@ffwll.ch>,
	Alex Deucher <alexander.deucher@amd.com>
Subject: Re: [Outreachy kernel] [PATCH] drm/amdgpu: use DEFINE_DEBUGFS_ATTRIBUTE with debugfs_create_file_unsafe()
Date: Fri, 30 Oct 2020 09:00:04 +0100	[thread overview]
Message-ID: <5a7d8e8d-8db5-ff56-6448-3f1cefc11ef8@amd.com> (raw)
In-Reply-To: <20201030075716.GA6976@my--box>

Am 30.10.20 um 08:57 schrieb Deepak R Varma:
> On Fri, Oct 30, 2020 at 08:11:20AM +0100, Greg KH wrote:
>> On Fri, Oct 30, 2020 at 08:52:45AM +0530, Deepak R Varma wrote:
>>> Using DEFINE_DEBUGFS_ATTRIBUTE macro with debugfs_create_file_unsafe()
>>> function in place of the debugfs_create_file() function will make the
>>> file operation struct "reset" aware of the file's lifetime. Additional
>>> details here: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.archive.carbon60.com%2Flinux%2Fkernel%2F2369498&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7Cddd7a6ac8164415a639708d87ca97004%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637396414464384011%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=o6GOHvMxNMuOPlC4nhDyURCHBLqfQZhYQq%2BiIMt3D3s%3D&amp;reserved=0
>>>
>>> Issue reported by Coccinelle script:
>>> scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>>>
>>> Signed-off-by: Deepak R Varma <mh12gx2825@gmail.com>
>>> ---
>>> Please Note: This is a Outreachy project task patch.
>>>
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 20 ++++++++++----------
>>>   1 file changed, 10 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>>> index 2d125b8b15ee..f076b1ba7319 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
>>> @@ -1551,29 +1551,29 @@ static int amdgpu_debugfs_sclk_set(void *data, u64 val)
>>>   	return 0;
>>>   }
>>>   
>>> -DEFINE_SIMPLE_ATTRIBUTE(fops_ib_preempt, NULL,
>>> -			amdgpu_debugfs_ib_preempt, "%llu\n");
>>> +DEFINE_DEBUGFS_ATTRIBUTE(fops_ib_preempt, NULL,
>>> +			 amdgpu_debugfs_ib_preempt, "%llu\n");
>> Are you sure this is ok?  Do these devices need this additional
>> "protection"?  Do they have the problem that these macros were written
>> for?
>>
>> Same for the other patches you just submitted here, I think you need to
>> somehow "prove" that these changes are necessary, checkpatch isn't able
>> to determine this all the time.
> Hi Greg,
> Based on my understanding, the current function debugfs_create_file()
> adds an overhead of lifetime managing proxy for such fop structs. This
> should be applicable to these set of drivers as well. Hence I think this
> change will be useful.

Well since this is only created once per device instance I don't really 
care about this little overhead.

But what exactly is debugfs doing or not doing here?

Regards,
Christian.

>
> I will wait for comments from other experts for driver specific
> consideration / behavior.
>
> Thanks,
> drv
>
>
>> thanks,
>>
>> greg k-h

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