linux-kernel - Re: [PATCH v2 07/19 5.15.y] minmax: simplify and clarify min_t()/max

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Message-ID: <2025100648-capable-register-101b@gregkh>
Date: Mon, 6 Oct 2025 12:47:45 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Eliav Farber <farbere@...zon.com>
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	Linus Torvalds <torvalds@...ux-foundation.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Subject: Re: [PATCH v2 07/19 5.15.y] minmax: simplify and clarify
 min_t()/max_t() implementation

On Fri, Oct 03, 2025 at 12:59:54PM +0000, Eliav Farber wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> 
> [ Upstream commit 017fa3e89187848fd056af757769c9e66ac3e93d ]
> 
> This simplifies the min_t() and max_t() macros by no longer making them
> work in the context of a C constant expression.
> 
> That means that you can no longer use them for static initializers or
> for array sizes in type definitions, but there were only a couple of
> such uses, and all of them were converted (famous last words) to use
> MIN_T/MAX_T instead.
> 
> Cc: David Laight <David.Laight@...lab.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Eliav Farber <farbere@...zon.com>

Eliav, your testing infrastructure needs some work, this patch breaks
the build on this kernel tree:

In file included from ./include/linux/kernel.h:16,
                 from ./include/linux/list.h:9,
                 from ./include/linux/wait.h:7,
                 from ./include/linux/wait_bit.h:8,
                 from ./include/linux/fs.h:6,
                 from fs/erofs/internal.h:10,
                 from fs/erofs/zdata.h:9,
                 from fs/erofs/zdata.c:6:
fs/erofs/zdata.c: In function ‘z_erofs_decompress_pcluster’:
fs/erofs/zdata.h:185:61: error: ISO C90 forbids variable length array ‘pages_onstack’ [-Werror=vla]
  185 |         min_t(unsigned int, THREAD_SIZE / 8 / sizeof(struct page *), 96U)
      |                                                             ^~~~
./include/linux/minmax.h:49:23: note: in definition of macro ‘__cmp_once_unique’
   49 |         ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
      |                       ^
./include/linux/minmax.h:164:27: note: in expansion of macro ‘__cmp_once’
  164 | #define min_t(type, x, y) __cmp_once(min, type, x, y)
      |                           ^~~~~~~~~~
fs/erofs/zdata.h:185:9: note: in expansion of macro ‘min_t’
  185 |         min_t(unsigned int, THREAD_SIZE / 8 / sizeof(struct page *), 96U)
      |         ^~~~~
fs/erofs/zdata.c:847:36: note: in expansion of macro ‘Z_EROFS_VMAP_ONSTACK_PAGES’
  847 |         struct page *pages_onstack[Z_EROFS_VMAP_ONSTACK_PAGES];
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors


I'll drop this whole series, please do a bit more testing before sending
out a new version.

thanks,

greg k-h