Re: [linux-next:master 7919/9290] include/linux/compiler_types.h:631:38: error: call to '__compiletime_assert_639' declared with attribute error: clamp() low limit pg.start greater than high limit pg.end

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 23 Jan 2026 15:31:08 -0800 Ankur Arora <ankur.a.arora@oracle.com> wrote:

> 
> kernel test robot <lkp@intel.com> writes:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head:   a0c666c25aeefd16f4b088c6549a6fb6b65a8a1d
> > commit: 93552c9a3350fff06543da18e4c80d3e804191ca [7919/9290] mm: folio_zero_user: cache neighbouring pages
> > config: riscv-randconfig-002-20260124 (https://download.01.org/0day-ci/archive/20260124/202601240453.QCjgGdJa-lkp@intel.com/config)
> > compiler: riscv64-linux-gcc (GCC) 8.5.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260124/202601240453.QCjgGdJa-lkp@intel.com/reproduce)
> 
> Oddly enough I'm unable to reproduce this with:
>    ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- make O=build_dir/ W=1 mm/

I couldn't.  gcc-15.2.0.

> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202601240453.QCjgGdJa-lkp@intel.com/
> >
> > All errors (new ones prefixed by >>):
> >
> >    In file included from include/linux/mm.h:18,
> >                     from arch/riscv/include/asm/sections.h:9,
> >                     from include/linux/interrupt.h:22,
> >                     from include/linux/kernel_stat.h:8,
> >                     from mm/memory.c:42:
> >    mm/memory.c: In function 'folio_zero_user':
> >>> include/linux/compiler_types.h:631:38: error: call to '__compiletime_assert_639' declared with attribute error: clamp() low limit pg.start greater than high limit pg.end
> 
> I'm a bit puzzled by this assert.
> 
> folio_zero_user():
>    {
> 	const unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio));
> 	const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE;
> 	const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);
> 	const int radius = FOLIO_ZERO_LOCALITY_RADIUS;
> 	struct range r[3];
> 	int i;
> 
> 	/*
> 	 * Faulting page and its immediate neighbourhood. Will be cleared at the
> 	 * end to keep its cachelines hot.
> 	 */
> 	r[2] = DEFINE_RANGE(clamp_t(s64, fault_idx - radius, pg.start, pg.end),
> 			    clamp_t(s64, fault_idx + radius, pg.start, pg.end));

This line expands to 2846 bytes of C.  The clamp()y functions are asking a lot
of the compiler - their development was drama-filled.

If we want to work around this (and I guess we should) then simply
open-coding these operations would be a good approach?