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 commit 0cc3b0ec23ce ("Clarify (and fix) in 4.13 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@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 43700480d897d48eb5dbdb879d9d1c5efddb8d0d..bcf64e92ffb05ba38c047e5d407bc0866b1ef1e2 100644 (file)
--- a/mm/filemap.c
+++ b/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();