[Intel-gfx] [PATCH 1/2] drm: share drm_add_fake_info_node

[Daniel Vetter]

On Wed, Jan 15, 2014 at 9:39 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Jan 15, 2014 at 12:40 AM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
>> On Wed, Jan 15, 2014 at 12:25:10AM +0100, Daniel Vetter wrote:
>>> On Tue, Jan 14, 2014 at 06:14:06AM -0800, Ben Widawsky wrote:
>>> > Both i915 and Armada had the exact same implementation. For an upcoming
>>> > patch, I'd like to call this function from two different source files in
>>> > i915, and having it available externally helps there too.
>>> >
>>> > While moving, add 'debugfs_' to the name in order to match the other drm
>>> > debugfs helper functions.
>>> >
>>> > Cc: linux-arm-kernel at lists.infradead.org
>>> > Cc: intel-gfx at lists.freedesktop.org
>>> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
>>>
>>> drm_debugfs_create_files in drm_debugfs.c has the almost same code again.
>>> Now the problem here is that the interface is a bit botched up, since all
>>> the users in i915 and armada actaully faile to clean up teh debugfs dentry
>>> if drm_add_fake_info_node.
>>
>> That's not correct - armada does clean up these, I think you need to
>> take a closer look at the code.
>>
>> We do this by setting node->info_ent to the file operations structure,
>> which is a unique key to the file being registered.
>>
>> Upon failure to create the fake node, we appropriately call
>> drm_debugfs_remove_files() with the first argument being a pointer to
>> the file operations.  This causes drm_debugfs_remove_files() to match
>> the fake entry, call debugfs_remove() on the dentry, and remove the
>> node from the list, and free the node structure we allocated.
>>
>> Upon driver teardown, we also call drm_debugfs_remove_files() but with
>> each fops which should be registered, thus cleaning up each fake node
>> which was created.
>>
>> So, Armada does clean up these entries properly.
>
> Indeed I've missed that and it's just i915 that botches this. I still
> think the helper would be saner if it cleans up all its leftovers in
> the failure case.

Ok, now I've actually page all the stuff back in - if
drm_add_fake_info_node fails we don't set up a drm_info_node structure
and link it anywhere. Which means drm_debugfs_remove_files won't ever
find it and hence can't possibly call debugfs_remove. Which means the
debugfs dentry is leaked. So I think the semantics of that new debugfs
helper should get fixed to also allocate and clean up the debugfs
node.

I agree that i915 is even worse since it doesn't bother to clean up
any debugfs files at all in the failure case.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch