Re: [PATCH 2/3] container_of: remove useless pair of parentheses

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

On Wed, Jul 15, 2026 at 04:51:28PM +0200, Vincent Mailhol wrote:
> On 15/07/2026 at 16:30, Alexey Dobriyan wrote:
> > On Tue, Jul 14, 2026 at 08:18:02PM +0200, Vincent Mailhol wrote:
> >> The last expression in container_of() doesn't need an extra pair of
> >> parenthesis. Remove it.
> >>
> >> Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
> >> ---
> >>  include/linux/container_of.h | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
> >> index 28500a62ab7e..68153170db32 100644
> >> --- a/include/linux/container_of.h
> >> +++ b/include/linux/container_of.h
> >> @@ -21,7 +21,7 @@
> >>  	static_assert(__same_type(*(ptr), typeof_member(type, member)) || \
> >>  		      __same_type(*(ptr), void),			\
> >>  		      "pointer type mismatch in container_of()");	\
> >> -	((type *)(__mptr - offsetof(type, member))); })
> >> +	(type *)(__mptr - offsetof(type, member)); })
> > 
> > container_of_const() has the same problem.
> 
> Yes. But scoped I my series to the container_of() macro only.
> 
> I don't plan to send a follow-up patch to remove the other useless
> parenthesis. The things which really bothered me was the __mptr
> variable which I removed in patch #3. And with that, I am done with
> what I wanted to contribute in this file.
> 
> But you are welcome to do this clean-up if you feel the need for it.
> 
> > And it should parenthesize first argument to _Generic.
> 
> Do you mean like this:
> 
> 	#define container_of_const(ptr, type, member)				\
> 		_Generic((ptr),							\
> 			const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
> 			default: ((type *)container_of(ptr, type, member))	\
> 		)
> 
> ?
> 
> Why would parenthesis be needed here? I don't see what kind of
> expression would make the current implementation unsafe.

It took me a while working with container_of_const() to get it right
with the (), so be careful removing any.

thanks,

greg k-h