ftrace: Remove unnecessary disabling of irqs

The disabling of interrupts around ftrace_update_code() was used
to protect against the evil ftrace daemon from years past. But that
daemon has long been killed. It is safe to keep interrupts enabled
while updating the initial mcount into nops.

The ftrace_mutex is also held which keeps other users at bay.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -2707,7 +2707,6 @@ static int ftrace_process_locs(struct module *mod,
 {
 	unsigned long *p;
 	unsigned long addr;
-	unsigned long flags;
 
 	mutex_lock(&ftrace_lock);
 	p = start;
@@ -2724,10 +2723,7 @@ static int ftrace_process_locs(struct module *mod,
 		ftrace_record_ip(addr);
 	}
 
-	/* disable interrupts to prevent kstop machine */
-	local_irq_save(flags);
 	ftrace_update_code(mod);
-	local_irq_restore(flags);
 	mutex_unlock(&ftrace_lock);
 
 	return 0;