Re: [PATCH -next] MIPS: fix debugfs_simple_attr.cocci warnings

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jan 25, 2019 at 03:43:21PM +0800, YueHaibing wrote:
> On 2019/1/25 15:11, Greg Kroah-Hartman wrote:
> > On Fri, Jan 25, 2019 at 02:42:17AM +0000, YueHaibing wrote:
> >> Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
> >> for debugfs files.
> >>
> >> Semantic patch information:
> >> Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
> >> imposes some significant overhead as compared to
> >> DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().
> > 
> > What kind of overhead is this adding, and how are you measuring it?
> 
> The log message on the commit introducing the semantic patch says the
> following:
> 
> commit 5103068eaca2 ("debugfs, coccinelle: check for obsolete DEFINE_SIMPLE_ATTRIBUTE() usage")
> 
>     In order to protect against file removal races, debugfs files created via
>     debugfs_create_file() now get wrapped by a struct file_operations at their
>     opening.
> 
>     If the original struct file_operations are known to be safe against removal
>     races by themselves already, the proxy creation may be bypassed by creating
>     the files through debugfs_create_file_unsafe().
> 
>     In order to help debugfs users who use the common
>       DEFINE_SIMPLE_ATTRIBUTE() + debugfs_create_file()
>     idiom to transition to removal safe struct file_operations, the helper
>     macro DEFINE_DEBUGFS_ATTRIBUTE() has been introduced.
> 
>     Thus, the preferred strategy is to use
>       DEFINE_DEBUGFS_ATTRIBUTE() + debugfs_create_file_unsafe()
>     now.


That is true.  So, are you saying that you "know" when you remove these
files everything is safe?  Are you seeing some sort of problem with
these files as-is?  If not, why change them to the "unsafe" method?

thanks,

greg k-h