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Subject[PATCH] mm/shmem: Do not wait for lock_page() in shmem_unused_huge_shrink()
Date
shmem_unused_huge_shrink() gets called from reclaim path. Waiting for page
lock may lead to deadlock there.

Replace lock_page() with trylock_page() and skip the page if we failed
to lock it. We will get to the page on the next scan.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure")
Cc: stable@vger.kernel.org # v4.8+
---
mm/shmem.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 1907688b75ee..2afe809d4bd4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -498,31 +498,42 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
continue;
}

- page = find_lock_page(inode->i_mapping,
+ page = find_get_page(inode->i_mapping,
(inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
if (!page)
goto drop;

+ /* No huge page at the end of the file: nothing to split */
if (!PageTransHuge(page)) {
- unlock_page(page);
put_page(page);
goto drop;
}

+ /*
+ * Leave the inode on the list if we failed to lock
+ * the page at this time.
+ *
+ * Waiting for the lock may lead to deadlock in the
+ * reclaim path.
+ */
+ if (!trylock_page(page)) {
+ put_page(page);
+ goto leave;
+ }
+
ret = split_huge_page(page);
unlock_page(page);
put_page(page);

- if (ret) {
- /* split failed: leave it on the list */
- iput(inode);
- continue;
- }
+ /* If split failed leave the inode on the list */
+ if (ret)
+ goto leave;

split++;
drop:
list_del_init(&info->shrinklist);
removed++;
+leave:
iput(inode);
}

--
2.16.1
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