[PATCH] mm: remove_mapping() safeness

Some users of remove_mapping had been unsafe.

Modify the remove_mapping precondition to ensure the caller has locked the
page and obtained the correct mapping.  Modify callers to ensure the
mapping is the correct one.

[hugh@veritas.com: swapper_space fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 41a3da3d6ccc..16180587fd7d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -377,8 +377,8 @@ static pageout_t pageout(struct page *page, struct address_space *mapping)
 
 int remove_mapping(struct address_space *mapping, struct page *page)
 {
-        if (!mapping)
-                return 0;               /* truncate got there first */
+        BUG_ON(!PageLocked(page));
+        BUG_ON(mapping != page_mapping(page));
 
         write_lock_irq(&mapping->tree_lock);
 
@@ -547,7 +547,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                                 goto free_it;
                 }
 
-                if (!remove_mapping(mapping, page))
+                if (!mapping || !remove_mapping(mapping, page))
                         goto keep_locked;
 
 free_it: