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@xxxxxxxxx>
---
mm/filemap.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c 2010-11-11 18:51:51.000000000 +1100
+++ linux-2.6/mm/filemap.c 2010-11-11 18:51:52.000000000 +1100
@@ -835,9 +835,6 @@ unsigned find_get_pages_contig(struct ad
if (radix_tree_deref_retry(page))
goto restart;
- if (page->mapping == NULL || page->index != index)
- break;
-
if (!page_cache_get_speculative(page))
goto repeat;
@@ -847,6 +844,16 @@ unsigned find_get_pages_contig(struct ad
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++;
--
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