Commit 10dd3ebe authored Mar 06, 2009 by KOSAKI Motohiro Committed by Ingo Molnar Mar 06, 2009

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 e6ea44e9 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>

parent 422d3c7a

kernel/trace/ftrace.c

+1 −6

Original line number	Diff line number	Diff line
		@@ -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 */

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