kprobes: Warn if the kprobe is reregistered

Warn if the kprobe is reregistered, since there must be
a software bug (actively used resource must not be re-registered)
and caller must be fixed.

Link: https://lkml.kernel.org/r/161236436734.194052.4058506306336814476.stgit@devnote2Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@linux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/kprobes.c

@@ -1520,13 +1520,16 @@ static struct kprobe *__get_valid_kprobe(struct kprobe *p)
 	return ap;
 }
 
-/* Return error if the kprobe is being re-registered */
-static inline int check_kprobe_rereg(struct kprobe *p)
+/*
+ * Warn and return error if the kprobe is being re-registered since
+ * there must be a software bug.
+ */
+static inline int warn_kprobe_rereg(struct kprobe *p)
 {
 	int ret = 0;
 
 	mutex_lock(&kprobe_mutex);
-	if (__get_valid_kprobe(p))
+	if (WARN_ON_ONCE(__get_valid_kprobe(p)))
 		ret = -EINVAL;
 	mutex_unlock(&kprobe_mutex);
 
@@ -1614,7 +1617,7 @@ int register_kprobe(struct kprobe *p)
 		return PTR_ERR(addr);
 	p->addr = addr;
 
-	ret = check_kprobe_rereg(p);
+	ret = warn_kprobe_rereg(p);
 	if (ret)
 		return ret;
 
@@ -1995,7 +1998,7 @@ int register_kretprobe(struct kretprobe *rp)
 		return ret;
 
 	/* If only rp->kp.addr is specified, check reregistering kprobes */
-	if (rp->kp.addr && check_kprobe_rereg(&rp->kp))
+	if (rp->kp.addr && warn_kprobe_rereg(&rp->kp))
 		return -EINVAL;
 
 	if (kretprobe_blacklist_size) {