[ Upstream commit 0919e1b69ab459e06df45d3ba6658d281962db80 ]
When a huge page is allocated, PagePrivate() is set if the allocation consumed a reservation. When freeing a huge page, PagePrivate is checked. If set, it indicates the reservation should be restored. PagePrivate being set at free huge page time mostly happens on error paths.
When huge page reservations are created, a check is made to determine if the mapping is associated with an explicitly mounted filesystem. If so, pages are also reserved within the filesystem. The default action when freeing a huge page is to decrement the usage count in any associated explicitly mounted filesystem. However, if the reservation is to be restored the reservation/use count within the filesystem should not be decrementd. Otherwise, a subsequent page allocation and free for the same mapping location will cause the file filesystem usage to go 'negative'.
Filesystem Size Used Avail Use% Mounted on nodev 4.0G -4.0M 4.1G - /opt/hugepool
To fix, when freeing a huge page do not adjust filesystem usage if PagePrivate() is set to indicate the reservation should be restored.
I did not cc stable as the problem has been around since reserves were added to hugetlbfs and nobody has noticed.
Link: http://lkml.kernel.org/r/20190328234704.27083-2-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Reviewed-by: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Michal Hocko mhocko@kernel.org Cc: "Kirill A . Shutemov" kirill.shutemov@linux.intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/hugetlb.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 6b03cd9b6d37..9914da93069e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1247,12 +1247,23 @@ void free_huge_page(struct page *page) ClearPagePrivate(page);
/* - * A return code of zero implies that the subpool will be under its - * minimum size if the reservation is not restored after page is free. - * Therefore, force restore_reserve operation. + * If PagePrivate() was set on page, page allocation consumed a + * reservation. If the page was associated with a subpool, there + * would have been a page reserved in the subpool before allocation + * via hugepage_subpool_get_pages(). Since we are 'restoring' the + * reservtion, do not call hugepage_subpool_put_pages() as this will + * remove the reserved page from the subpool. */ - if (hugepage_subpool_put_pages(spool, 1) == 0) - restore_reserve = true; + if (!restore_reserve) { + /* + * A return code of zero implies that the subpool will be + * under its minimum size if the reservation is not restored + * after page is free. Therefore, force restore_reserve + * operation. + */ + if (hugepage_subpool_put_pages(spool, 1) == 0) + restore_reserve = true; + }
spin_lock(&hugetlb_lock); clear_page_huge_active(page);