From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>, stable@vger.kernel.org
Subject: [PATCH] mm: Remove bogus VM_BUG_ON
Date: Wed, 18 Aug 2021 15:49:32 +0100 [thread overview]
Message-ID: <20210818144932.940640-1-willy@infradead.org> (raw)
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
next reply other threads:[~2021-08-18 14:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 14:49 Matthew Wilcox (Oracle) [this message]
2021-08-18 16:34 ` [PATCH] mm: Remove bogus VM_BUG_ON Hugh Dickins
2021-08-18 16:45 ` Matthew Wilcox
2021-08-19 20:42 ` Hugh Dickins
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