mm: find_get_pages_contig fixlet
Testing ->mapping and ->index without a ref is not stable as the page
may have been reused at this point.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index ca38939..1a3dd59 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -837,9 +837,6 @@
if (radix_tree_deref_retry(page))
goto restart;
- if (page->mapping == NULL || page->index != index)
- break;
-
if (!page_cache_get_speculative(page))
goto repeat;
@@ -849,6 +846,16 @@
goto repeat;
}
+ /*
+ * must check mapping and index after taking the ref.
+ * otherwise we can get both false positives and false
+ * negatives, which is just confusing to the caller.
+ */
+ if (page->mapping == NULL || page->index != index) {
+ page_cache_release(page);
+ break;
+ }
+
pages[ret] = page;
ret++;
index++;
