mm: fix for negative counter: nr_file_hugepages

While qualifiying the 6.4 release, the following warning was detected in
messages:

vmstat_refresh: nr_file_hugepages -15664

The warning is caused by the incorrect updating of the NR_FILE_THPS
counter in the function split_huge_page_to_list.  The if case is checking
for folio_test_swapbacked, but the else case is missing the check for
folio_test_pmd_mappable.  The other functions that manipulate the counter
like __filemap_add_folio and filemap_unaccount_folio have the
corresponding check.

I have a test case, which reproduces the problem. It can be found here:
  https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c

The test case reproduces on an XFS filesystem. Running the same test
case on a BTRFS filesystem does not reproduce the problem.

AFAIK version 6.1 until 6.6 are affected by this problem.

[[email protected]: whitespace fix]
[[email protected]: test for folio_test_pmd_mappable()]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Stefan Roesch <[email protected]>
Co-debugged-by: Johannes Weiner <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions