mm: fix for negative counter: nr_file_hugepages

commit a48d5bdc877b85201e42cef9c2fdf5378164c23a upstream.

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.

[akpm@linux-foundation.org: whitespace fix]
[shr@devkernel.io: test for folio_test_pmd_mappable()]
Link: https://lkml.kernel.org/r/20231108171517.2436103-1-shr@devkernel.io
Link: https://lkml.kernel.org/r/20231106181918.1091043-1-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Co-debugged-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 064fbd9..874000f 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2737,13 +2737,15 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
                        int nr = folio_nr_pages(folio);
 
                        xas_split(&xas, folio, folio_order(folio));
-                       if (folio_test_swapbacked(folio)) {
-                               __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
-                                                       -nr);
-                       } else {
-                               __lruvec_stat_mod_folio(folio, NR_FILE_THPS,
-                                                       -nr);
-                               filemap_nr_thps_dec(mapping);
+                       if (folio_test_pmd_mappable(folio)) {
+                               if (folio_test_swapbacked(folio)) {
+                                       __lruvec_stat_mod_folio(folio,
+                                                       NR_SHMEM_THPS, -nr);
+                               } else {
+                                       __lruvec_stat_mod_folio(folio,
+                                                       NR_FILE_THPS, -nr);
+                                       filemap_nr_thps_dec(mapping);
+                               }
                        }
                }