[PATCH] kprobes: fix race in aggregate kprobe registration

When registering multiple kprobes at the same address, we leave a small
window where the kprobe hlist will not contain a reference to the
registered kprobe, leading to potentially, a system crash if the breakpoint
is hit on another processor.

Patch below now automically relpace the old kprobe with the new
kprobe from the hash list.
Signed-off-by: NAnil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Acked-by: NAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/kprobes.c

@@ -399,10 +399,7 @@ static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 	INIT_LIST_HEAD(&ap->list);
 	list_add_rcu(&p->list, &ap->list);
 
-	INIT_HLIST_NODE(&ap->hlist);
-	hlist_del_rcu(&p->hlist);
-	hlist_add_head_rcu(&ap->hlist,
-		&kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
+	hlist_replace_rcu(&p->hlist, &ap->hlist);
 }
 
 /*