From: Matthew Wilcox (Oracle) <willy@infradead.org>
Date: Wed, 18 Aug 2021 14:43:41 +0000 (-0400)
Subject: mm: Remove bogus VM_BUG_ON
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=51cbb3f3ce31fc203f185fc3d92dae0e56b5aab3;p=users%2Fwilly%2Flinux.git

mm: Remove bogus VM_BUG_ON

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.

Cc: stable@vger.kernel.org
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---

diff --git a/mm/filemap.c b/mm/filemap.c
index dae481293b5d9..82a17c35eb96b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2093,7 +2093,6 @@ 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))