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function trace: fix a bug of single thread function trace 

Impact: fix "no output from tracer" bug caused by ftrace_update_pid_func()

When disabling single thread function trace using
"echo -1 > set_ftrace_pid", the normal function trace
has to restore to original function, otherwise the normal
function trace will not work well.

Without this commit, something like below:

	$ ps |grep 850
	  850 root      2556 S    -/bin/sh
	$ echo 850 > /debug/tracing/set_ftrace_pid
	$ echo function > /debug/tracing/current_tracer
	$ echo 1 > /debug/tracing/tracing_enabled
	$ sleep 1
	$ echo 0 > /debug/tracing/tracing_enabled
	$ cat /debug/tracing/trace_pipe |wc -l
	59704
	$ echo -1 > /debug/tracing/set_ftrace_pid
	$ echo 1 > /debug/tracing/tracing_enabled
	$ sleep 1
	$ echo 0 > /debug/tracing/tracing_enabled
	$ more /debug/tracing/trace_pipe
		<====== nothing output now!
			it should output trace record.

Signed-off-by: Liming Wang <liming.wang@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Liming Wang 2008-12-02 10:33:08 +08:00 committed by Ingo Molnar
parent 222658e08f
commit 66eafebc10
1 changed files with 2 additions and 4 deletions
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6
kernel/trace/ftrace.c
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@ -243,10 +243,8 @@ static void ftrace_update_pid_func(void)
set_ftrace_pid_function(func);
func = ftrace_pid_func;
} else {
if (func != ftrace_pid_func)
goto out;
set_ftrace_pid_function(func);
if (func == ftrace_pid_func)
func = ftrace_pid_function;
}
#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST