+ mm-fix-for-negative-counter-nr_file_hugepages.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm: fix for negative counter: nr_file_hugepages
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-for-negative-counter-nr_file_hugepages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-for-negative-counter-nr_file_hugepages.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Stefan Roesch <shr@devkernel.io>
Subject: mm: fix for negative counter: nr_file_hugepages
Date: Mon, 6 Nov 2023 10:19:18 -0800

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.

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>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/huge_memory.c~mm-fix-for-negative-counter-nr_file_hugepages
+++ a/mm/huge_memory.c
@@ -2772,7 +2772,8 @@ int split_huge_page_to_list(struct page
 			if (folio_test_swapbacked(folio)) {
 				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
 							-nr);
-			} else {
+			} else if (folio_test_pmd_mappable(folio)) {
+
 				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
 							-nr);
 				filemap_nr_thps_dec(mapping);
_

Patches currently in -mm which might be from shr@devkernel.io are

mm-fix-for-negative-counter-nr_file_hugepages.patch