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tracing: fix deadlock when setting set_ftrace_pid 

Impact: fix deadlock while using set_ftrace_pid

Reproducer:

	# cd /sys/kernel/debug/tracing
	# echo $$ > set_ftrace_pid

	then, console becomes hung.

Details:

when writing set_ftracepid, kernel callstack is following

	ftrace_pid_write()
		mutex_lock(&ftrace_lock);
		ftrace_update_pid_func()
			mutex_lock(&ftrace_lock);
			mutex_unlock(&ftrace_lock);
		mutex_unlock(&ftrace_lock);

then, system always deadlocks when ftrace_pid_write() is called.

In past days, ftrace_pid_write() used ftrace_start_lock, but
commit e6ea44e9b4 consolidated
ftrace_start_lock to ftrace_lock.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <20090306151155.0778.A69D9226@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
KOSAKI Motohiro 2009-03-06 15:29:04 +09:00 committed by Ingo Molnar
parent 422d3c7a57
commit 10dd3ebe21
1 changed files with 1 additions and 6 deletions
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7
kernel/trace/ftrace.c
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@ -218,10 +218,8 @@ static void ftrace_update_pid_func(void)
{
ftrace_func_t func;
mutex_lock(&ftrace_lock);
if (ftrace_trace_function == ftrace_stub)
goto out;
return;
func = ftrace_trace_function;
@ -238,9 +236,6 @@ static void ftrace_update_pid_func(void)
#else
__ftrace_trace_function = func;
#endif
out:
mutex_unlock(&ftrace_lock);
}
/* set when tracing only a pid */