Re: [akpm-mm:mm-unstable 36/67] mm/khugepaged.c:2337:7: error: implicit declaration of function 'folio_expected_ref_count'; did you mean 'folio_ref_count'?

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

On Wed, 28 May 2025 18:04:02 +0530 Shivank Garg <shivankg@amd.com> wrote:

> On 5/28/2025 5:46 PM, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> > head:   52ce652e7ab0f015b51fee11b2862507b2c0c25d
> > commit: 3bdddbba5f02f6d97283acb18e2a6e079324fe4b [36/67] mm/khugepaged: fix race with folio split/free using temporary reference
> > config: arm64-randconfig-002-20250528 (https://download.01.org/0day-ci/archive/20250528/202505282015.F0fVmLmH-lkp@intel.com/config)
> > compiler: aarch64-linux-gcc (GCC) 7.5.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250528/202505282015.F0fVmLmH-lkp@intel.com/reproduce)
> > 
> > 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/202505282015.F0fVmLmH-lkp@intel.com/
> > 
> > Note: the akpm-mm/mm-unstable HEAD 52ce652e7ab0f015b51fee11b2862507b2c0c25d builds fine.
> >       It only hurts bisectability.
> > 
> > All errors (new ones prefixed by >>):
> > 
> >    mm/khugepaged.c: In function 'hpage_collapse_scan_file':
> >>> mm/khugepaged.c:2337:7: error: implicit declaration of function 'folio_expected_ref_count'; did you mean 'folio_ref_count'? [-Werror=implicit-function-declaration]
> >       if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) {
> >           ^~~~~~~~~~~~~~~~~~~~~~~~
> >           folio_ref_count
> >    cc1: some warnings being treated as errors
> > 
> > 
> > vim +2337 mm/khugepaged.c
> 
> folio_expected_ref_count() is introduced with this commit[1] and merged into mm-* tree.
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-unstable&id=86ebd50224c0734d965843260d0dc057a9431c61
> 

Well darn.  We have a patch in mm-hotfixes-unstable which is cc:stable
(mm-khugepaged-fix-race-with-folio-split-free-using-temporary-reference.patch)
which is dependent upon a patch
(mm-add-folio_expected_ref_count-for-reference-count-calculation.patch)
which is scheduled for 6.16-rc1.

I'll move
mm-khugepaged-fix-race-with-folio-split-free-using-temporary-reference.patch
into mm-stable, after
mm-add-folio_expected_ref_count-for-reference-count-calculation.patch
to remove the bisection hole.  This means that when the -stable
maintainers try to backport
mm-khugepaged-fix-race-with-folio-split-free-using-temporary-reference.patch
into earlier kernels, the build will fail.  When this happens, please
work with them to come up with a version of
mm-khugepaged-fix-race-with-folio-split-free-using-temporary-reference.patch
which is suitable for 6.15 and earlier.