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

[Ankur Arora <ankur.a.arora@oracle.com>]

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/

> 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));

the cause of the failure is that the compiler decides that pg.start > pg.end in:
  clamp_t(s64, fault_idx + radius, pg.start, pg.end));

which come from:
	const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);

Now pg.start > pg.end if, folio_nr_pages() == 1.

Which would need folio_test_large() to evaluate to false at compile time:
  static inline unsigned long folio_nr_pages(const struct folio *folio)
  {
	if (!folio_test_large(folio))
		return 1;
	return folio_large_nr_pages(folio);
  }

But folio_test_large() is only defined as a test_bit(), without a
compile time constant defintion.

Also, the configuration has HUGETLBFS (which anyway guards the
definition of folio_zero_user()):

     $ cat config |egrep 'HUGETLBFS|TRANSPARENT'
     CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
     CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD=y
     # CONFIG_TRANSPARENT_HUGEPAGE is not set
     CONFIG_ARCH_SUPPORTS_HUGETLBFS=y
     CONFIG_HUGETLBFS=y

Ankur

>      _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>                                          ^
>    include/linux/range.h:46:11: note: in definition of macro 'DEFINE_RANGE'
>       .end = (_end),   \
>               ^~~~
>    include/linux/compiler_types.h:619:2: note: in expansion of macro '__compiletime_assert'
>      __compiletime_assert(condition, msg, prefix, suffix)
>      ^~~~~~~~~~~~~~~~~~~~
>    include/linux/compiler_types.h:631:2: note: in expansion of macro '_compiletime_assert'
>      _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>      ^~~~~~~~~~~~~~~~~~~
>    include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
>     #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                         ^~~~~~~~~~~~~~~~~~
>    include/linux/minmax.h:188:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
>      BUILD_BUG_ON_MSG(statically_true(ulo > uhi),    \
>      ^~~~~~~~~~~~~~~~
>    include/linux/minmax.h:195:2: note: in expansion of macro '__clamp_once'
>      __clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_))
>      ^~~~~~~~~~~~
>    include/linux/minmax.h:218:36: note: in expansion of macro '__careful_clamp'
>     #define clamp_t(type, val, lo, hi) __careful_clamp(type, val, lo, hi)
>                                        ^~~~~~~~~~~~~~~
>    mm/memory.c:7296:8: note: in expansion of macro 'clamp_t'
>            clamp_t(s64, fault_idx + radius, pg.start, pg.end));
>            ^~~~~~~
>
>
> vim +/__compiletime_assert_639 +631 include/linux/compiler_types.h
>
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  617
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  618  #define _compiletime_assert(condition, msg, prefix, suffix) \
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  619  	__compiletime_assert(condition, msg, prefix, suffix)
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  620
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  621  /**
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  622   * compiletime_assert - break build and emit msg if condition is false
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  623   * @condition: a compile-time constant condition to check
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  624   * @msg:       a message to emit if condition is false
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  625   *
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  626   * In tradition of POSIX assert, this macro will break the build if the
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  627   * supplied condition is *false*, emitting the supplied error message if the
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  628   * compiler has support to do so.
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  629   */
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  630  #define compiletime_assert(condition, msg) \
> eb5c2d4b45e3d2 Will Deacon 2020-07-21 @631  	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> eb5c2d4b45e3d2 Will Deacon 2020-07-21  632
>
> :::::: The code at line 631 was first introduced by commit
> :::::: eb5c2d4b45e3d2d5d052ea6b8f1463976b1020d5 compiler.h: Move compiletime_assert() macros into compiler_types.h
>
> :::::: TO: Will Deacon <will@kernel.org>
> :::::: CC: Will Deacon <will@kernel.org>