[PATCH] fix klist semantics for lists which have elements removed on traversal

The problem is that klists claim to provide semantics for safe traversal of
lists which are being modified.  The failure case is when traversal of a
list causes element removal (a fairly common case).  The issue is that
although the list node is refcounted, if it is embedded in an object (which
is universally the case), then the object will be freed regardless of the
klist refcount leading to slab corruption because the klist iterator refers
to the prior element to get the next.

The solution is to make the klist take and release references to the
embedding object meaning that the embedding object won't be released until
the list relinquishes the reference to it.

(akpm: fast-track this because it's needed for the 2.6.13 scsi merge)

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/include/linux/klist.h b/include/linux/klist.h
index c4d1fae4dd89..74071254c9d3 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -17,15 +17,17 @@
 #include <linux/kref.h>
 #include <linux/list.h>
 
-
+struct klist_node;
 struct klist {
         spinlock_t              k_lock;
         struct list_head        k_list;
+        void                    (*get)(struct klist_node *);
+        void                    (*put)(struct klist_node *);
 };
 
 
-extern void klist_init(struct klist * k);
-
+extern void klist_init(struct klist * k, void (*get)(struct klist_node *),
+                       void (*put)(struct klist_node *));
 
 struct klist_node {
         struct klist            * n_klist;