list_debug: WARN for adding something already in the list

We were bitten by this at one point and added an additional sanity test
for DEBUG_LIST.  You can't validly add a list_head to a list where either
prev or next is the same as the thing you're adding.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/list_debug.c b/lib/list_debug.c
index 3810b481f940..23a5e031cd8b 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -31,6 +31,9 @@ void __list_add(struct list_head *new,
                 "list_add corruption. prev->next should be "
                 "next (%p), but was %p. (prev=%p).\n",
                 next, prev->next, prev);
+        WARN(new == prev || new == next,
+             "list_add double add: new=%p, prev=%p, next=%p.\n",
+             new, prev, next);
         next->prev = new;
         new->next = next;
         new->prev = prev;