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* [PATCH] mm: Remove bogus VM_BUG_ON
@ 2021-08-18 14:49 Matthew Wilcox (Oracle)
  2021-08-18 16:34 ` Hugh Dickins
  0 siblings, 1 reply; 4+ messages in thread
From: Matthew Wilcox (Oracle) @ 2021-08-18 14:49 UTC (permalink / raw)
  To: Andrew Morton, linux-mm, linux-kernel; +Cc: Matthew Wilcox (Oracle), stable

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

diff --git a/mm/filemap.c b/mm/filemap.c
index d1458ecf2f51..34de0b14aaa9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2033,17 +2033,16 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
 	XA_STATE(xas, &mapping->i_pages, start);
 	struct page *page;
 
 	rcu_read_lock();
 	while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
 		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))
 				goto put;
 			if (page->mapping != mapping || PageWriteback(page))
 				goto unlock;
 			VM_BUG_ON_PAGE(!thp_contains(page, xas.xa_index),
 					page);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-08-19 20:43 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-08-18 14:49 [PATCH] mm: Remove bogus VM_BUG_ON Matthew Wilcox (Oracle)
2021-08-18 16:34 ` Hugh Dickins
2021-08-18 16:45   ` Matthew Wilcox
2021-08-19 20:42     ` Hugh Dickins

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