[patch 048/262] mm/filemap.c: remove bogus VM_BUG_ON

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From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm/filemap.c: 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.

Link: https://lkml.kernel.org/r/20210818144932.940640-1-willy@xxxxxxxxxxxxx
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reported-by: <syzbot+c87be4f669d920c76330@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/filemap.c |    1 -
 1 file changed, 1 deletion(-)

--- a/mm/filemap.c~mm-remove-bogus-vm_bug_on
+++ a/mm/filemap.c
@@ -2093,7 +2093,6 @@ 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))
_



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