Name: Group Reference Counting Debug Patch
Status: Tested on 21 May 2004

Someone is dropping refcnt of current->group_info too many times.
This should catch the culprit.

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .14959-linux-ppc64-2.5/include/linux/sched.h .14959-linux-ppc64-2.5.updated/include/linux/sched.h
--- .14959-linux-ppc64-2.5/include/linux/sched.h	2004-05-18 07:04:54.000000000 +1000
+++ .14959-linux-ppc64-2.5.updated/include/linux/sched.h	2004-05-21 11:06:50.000000000 +1000
@@ -365,11 +365,7 @@ struct group_info {
 	atomic_inc(&(group_info)->usage); \
 } while (0)
 
-#define put_group_info(group_info) do { \
-	if (atomic_dec_and_test(&(group_info)->usage)) \
-		groups_free(group_info); \
-} while (0)
-
+extern void put_group_info(struct group_info *);
 struct group_info *groups_alloc(int gidsetsize);
 void groups_free(struct group_info *group_info);
 int set_current_groups(struct group_info *group_info);
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .14959-linux-ppc64-2.5/kernel/sys.c .14959-linux-ppc64-2.5.updated/kernel/sys.c
--- .14959-linux-ppc64-2.5/kernel/sys.c	2004-05-20 22:05:02.000000000 +1000
+++ .14959-linux-ppc64-2.5.updated/kernel/sys.c	2004-05-21 11:12:54.000000000 +1000
@@ -1158,6 +1158,16 @@ out_undo_partial_alloc:
 
 EXPORT_SYMBOL(groups_alloc);
 
+void put_group_info(struct group_info *group_info)
+{
+	if (atomic_dec_and_test(&group_info->usage)) {
+		/* Can't free underneath ourselves. */
+		BUG_ON(group_info == current->group_info);
+		groups_free(group_info);
+	}
+}
+EXPORT_SYMBOL(put_group_info);
+
 void groups_free(struct group_info *group_info)
 {
 	if (group_info->blocks[0] != group_info->small_block) {
@@ -1268,6 +1278,8 @@ int set_current_groups(struct group_info
 	int retval;
 	struct group_info *old_info;
 
+	BUG_ON(atomic_read(&group_info->usage) <= 0);
+
 	retval = security_task_setgroups(group_info);
 	if (retval)
 		return retval;