[PATCH 5.14 807/849] mm/filemap.c: remove bogus VM_BUG_ON

Greg Kroah-Hartman
2021-11-16T01:16:09Z

From: Matthew Wilcox (Oracle) <willy@infradead.org>

commit d417b49fff3e2f21043c834841e8623a6098741d upstream.

It is not safe to check page->index without holding the page lock. It
can be changed if the page is moved between the swap cache and the page
cache for a shmem file, for example. There is a VM_BUG_ON below which
checks page->index is correct after taking the page lock.

Link: https://lkml.kernel.org/r/20210818144932.940640-1-willy@infradead.org
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: <syzbot+c87be4f669d920c76330@syzkaller.appspotmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/filemap.c | 1 -
1 file changed, 1 deletion(-)

--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2038,7 +2038,6 @@ unsigned find_lock_entries(struct addres
if (!xa_is_value(page)) {
if (page->index < start)
goto put;
- VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
if (page->index + thp_nr_pages(page) - 1 > end)
goto put;
if (!trylock_page(page))