From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/filemap: fix find_lock_entries hang on 32-bit THP
No problem on 64-bit, or without huge pages, but xfstests generic/308 hung
uninterruptibly on 32-bit huge tmpfs. Since 4.13's 0cc3b0ec23ce ("Clarify
(and fix) MAX_LFS_FILESIZE macros"), MAX_LFS_FILESIZE is only a PAGE_SIZE
away from wrapping 32-bit xa_index to 0, so the new find_lock_entries()
has to be extra careful when handling a THP.
Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2104211735430.3299@eggly.anvils
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/mm/filemap.c~mm-filemap-fix-find_lock_entries-hang-on-32-bit-thp
+++ a/mm/filemap.c
@@ -1969,8 +1969,14 @@ unlock:
put:
put_page(page);
next:
- if (!xa_is_value(page) && PageTransHuge(page))
- xas_set(&xas, page->index + thp_nr_pages(page));
+ if (!xa_is_value(page) && PageTransHuge(page)) {
+ unsigned int nr_pages = thp_nr_pages(page);
+
+ /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
+ xas_set(&xas, page->index + nr_pages);
+ if (xas.xa_index < nr_pages)
+ break;
+ }
}
rcu_read_unlock();
_
