linux-kernel - Re: [PATCH] staging/android: sync_debug: unproxify debugfs files' fops

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Date:	Fri, 27 May 2016 11:15:41 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Nicolai Stange <nicstange@...il.com>
Cc:	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
Subject: Re: [PATCH] staging/android: sync_debug: unproxify debugfs files'
 fops

On Fri, May 27, 2016 at 08:03:54PM +0200, Nicolai Stange wrote:
> Since commit 49d200deaa68 ("debugfs: prevent access to removed files'
> private data"), a debugfs file's file_operations methods get proxied
> through lifetime aware wrappers.
> 
> However, only a certain subset of the file_operations members is supported
> by debugfs and ->compat_ioctl isn't among them -- it appears to be NULL
> from the VFS layer's perspective.
> 
> This behaviour breaks the /sys/kernel/debug/sync/sw_sync file introduced
> concurrently with commit a44eb74cd413 ("staging/android: move SW_SYNC_USER
> to a debugfs file").
> 
> Since that file never gets removed, there is no file removal race and thus,
> a lifetime checking proxy isn't needed.
> 
> Avoid the proxying for /sys/kernel/debug/sync/sw_sync by creating it via
> debugfs_create_file_unsafe() rather than debugfs_create_file().
> For consistency, do the same for /sys/kernel/debug/sync/info.
> 
> Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private
>                       data")
> Fixes: a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs
>                       file")
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> ---
>  Applicable to linux-next-20160527.
>  x86_64 allmodconfig build succeeds w/o any new warnings.
> 
>  Related discussion can be found here:
>  http://lkml.kernel.org/g/878tz22peb.fsf@gmail.com
> 
>  drivers/staging/android/sync_debug.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)

Thanks, will queue this up after 4.7-rc1 is out.

greg k-h