tracing: Fix stack tracer sysctl handling

This made my machine completely frozen:

  # echo 1 > /proc/sys/kernel/stack_tracer_enabled
  # echo 2 > /proc/sys/kernel/stack_tracer_enabled

The cause is register_ftrace_function() was called twice.

Also fix ftrace_enabled sysctl, though seems nothing bad happened
as I tested it.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A448D17.9010305@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 2d7aebd71dbd..e644af910124 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -326,10 +326,10 @@ stack_trace_sysctl(struct ctl_table *table, int write,
         ret = proc_dointvec(table, write, file, buffer, lenp, ppos);
 
         if (ret || !write ||
-            (last_stack_tracer_enabled == stack_tracer_enabled))
+            (last_stack_tracer_enabled == !!stack_tracer_enabled))
                 goto out;
 
-        last_stack_tracer_enabled = stack_tracer_enabled;
+        last_stack_tracer_enabled = !!stack_tracer_enabled;
 
         if (stack_tracer_enabled)
                 register_ftrace_function(&trace_ops);