On Fri 2017-01-06 14:07:34, Josh Poimboeuf wrote:

On Fri, Dec 23, 2016 at 11:18:03AM +0100, Petr Mladek wrote:

quoted

On Fri 2016-12-23 10:24:35, Miroslav Benes wrote:

quoted

quoted

quoted

quoted

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 5efa262..e79ebb5 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c

@@ -29,6 +29,7 @@
 #include <linux/bug.h>
 #include <linux/printk.h>
 #include "patch.h"
+#include "transition.h"
 
 static LIST_HEAD(klp_ops);
 

@@ -54,15 +55,53 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 {
 	struct klp_ops *ops;
 	struct klp_func *func;
+	int patch_state;
 
 	ops = container_of(fops, struct klp_ops, fops);
 
 	rcu_read_lock();
+
 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);
-	if (WARN_ON_ONCE(!func))
+
+	if (!func)
 		goto unlock;

Yeah, I'm thinking we should keep the warning to catch any bugs in case
any of our ftrace assumptions change.  Maybe I should add a comment:

	/*
	 * func can never be NULL because preemption should be disabled
	 * here and unregister_ftrace_function() does the equivalent of
	 * a synchronize_sched() before the func_stack removal.
	 */
	if (WARN_ON_ONCE(!func))
		goto unlock;

Sounds reasonable to me.

Best Regards,
Petr