Btrfs: ulist realloc bugfix

ulist_next gets the pointer to the previously returned element to find the
next element from there. However, when we call ulist_add while iteration
with ulist_next is in progress (ulist explicitly supports this), we can
realloc the ulist internal memory, which makes the pointer to the previous
element useless.

Instead, we now use an iterator parameter that's independent from the
internal pointers.

Reported-by: Alexander Block <ablock84@googlemail.com>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
index 2e25dec58ec0..62d2574f775a 100644
--- a/fs/btrfs/ulist.h
+++ b/fs/btrfs/ulist.h
@@ -24,6 +24,10 @@
  */
 #define ULIST_SIZE 16
 
+struct ulist_iterator {
+        int i;
+};
+
 /*
  * element of the list
  */
@@ -63,6 +67,9 @@ struct ulist *ulist_alloc(unsigned long gfp_mask);
 void ulist_free(struct ulist *ulist);
 int ulist_add(struct ulist *ulist, u64 val, unsigned long aux,
               unsigned long gfp_mask);
-struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_node *prev);
+struct ulist_node *ulist_next(struct ulist *ulist,
+                              struct ulist_iterator *uiter);
+
+#define ULIST_ITER_INIT(uiter) ((uiter)->i = 0)
 
 #endif