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);