The patch titled
Subject: mm/shmem: do not wait for lock_page() in shmem_unused_huge_shrink()
has been added to the -mm tree. Its filename is
mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: mm/shmem: do not wait for lock_page() in shmem_unused_huge_shrink()
shmem_unused_huge_shrink() gets called from reclaim path. Waiting for
page lock may lead to deadlock there.
There was a bug report that may be attributed to this:
http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@xxxxxxxxxxxxxxxxx
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.
We can test for the PageTransHuge() outside the page lock as we only need
protection against splitting the page under us. Holding pin oni the page
is enough for this.
Link: http://lkml.kernel.org/r/20180316210830.43738-1-kirill.shutemov@xxxxxxxxxxxxxxx
Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Eric Wheeler <linux-mm@xxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)
diff -puN mm/shmem.c~mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink mm/shmem.c
--- a/mm/shmem.c~mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink
+++ a/mm/shmem.c
@@ -493,36 +493,45 @@ next:
info = list_entry(pos, struct shmem_inode_info, shrinklist);
inode = &info->vfs_inode;
- if (nr_to_split && split >= nr_to_split) {
- iput(inode);
- continue;
- }
+ if (nr_to_split && split >= nr_to_split)
+ goto leave;
- 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);
}
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-khugepaged-convert-vm_bug_on-to-collapse-fail.patch
mm-thp-do-not-wait-for-lock_page-in-deferred_split_scan.patch
mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch