[PATCH 4.9 05/50] mm/khugepaged: collapse_shmem() stop if punched or truncated

Greg Kroah-Hartman
2018-12-04T11:11:20Z

commit 701270fa193aadf00bdcf607738f64997275d4c7 upstream.

Huge tmpfs testing showed that although collapse_shmem() recognizes a
concurrently truncated or hole-punched page correctly, its handling of
holes was liable to refill an emptied extent. Add check to stop that.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261522040.2275@eggly.anvils
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <stable@vger.kernel.org> [4.8+]
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/khugepaged.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1df37ee996d5..62de24194f24 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1351,6 +1351,16 @@ static void collapse_shmem(struct mm_struct *mm,
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
int n = min(iter.index, end) - index;

+ /*
+ * Stop if extent has been hole-punched, and is now completely
+ * empty (the more obvious i_size_read() check would take an
+ * irq-unsafe seqlock on 32-bit).
+ */
+ if (n >= HPAGE_PMD_NR) {
+ result = SCAN_TRUNCATED;
+ goto tree_locked;
+ }
+
/*
* Handle holes in the radix tree: charge it from shmem and
* insert relevant subpage of new_page into the radix-tree.
@@ -1462,6 +1472,11 @@ static void collapse_shmem(struct mm_struct *mm,
if (result == SCAN_SUCCEED && index < end) {
int n = end - index;

+ /* Stop if extent has been truncated, and is now empty */
+ if (n >= HPAGE_PMD_NR) {
+ result = SCAN_TRUNCATED;
+ goto tree_locked;
+ }
if (!shmem_charge(mapping->host, n)) {
result = SCAN_FAIL;
goto tree_locked;
--
2.17.1