From 72b38500a7217939f9788e3e182c4a7cbf5b5a50 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Fri, 5 Nov 2021 13:37:10 -0700
Subject: [PATCH] mm/filemap.c: remove bogus VM_BUG_ON

References: bsc#1190208 (MM functional and performance backports) stable-5.14.19
Patch-mainline: v5.16-rc1
Git-commit: d417b49fff3e2f21043c834841e8623a6098741d

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: Mel Gorman <mgorman@suse.de>
---
 mm/filemap.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 8ad61538c0b8..e3aa29fd32d3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2039,7 +2039,6 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
 		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))