Commit e0a413f6 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
Browse files

tracing: Warn on output if the function tracer was found corrupted 



As the function tracer is very intrusive, lots of self checks are
performed on the tracer and if something is found to be strange
it will shut itself down keeping it from corrupting the rest of the
kernel. This shutdown may still allow functions to be traced, as the
tracing only stops new modifications from happening. Trying to stop
the function tracer itself can cause more harm as it requires code
modification.

Although a WARN_ON() is executed, a user may not notice it. To help
the user see that something isn't right with the tracing of the system
a big warning is added to the output of the tracer that lets the user
know that their data may be incomplete.

Reported-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent e36de1de

kernel/trace/ftrace.c

+8 −0
Original line number Diff line number Diff line
@@ -3862,6 +3862,14 @@ void ftrace_kill(void) 
	clear_ftrace_function();

}



/**

 * Test if ftrace is dead or not.

 */

int ftrace_is_dead(void)

{

	return ftrace_disabled;

}



/**

 * register_ftrace_function - register a function for profiling

 * @ops - ops structure that holds the function for profiling.

kernel/trace/trace.c

+15 −0
Original line number Diff line number Diff line
@@ -2160,6 +2160,14 @@ void trace_default_header(struct seq_file *m) 
	}

}



static void test_ftrace_alive(struct seq_file *m)

{

	if (!ftrace_is_dead())

		return;

	seq_printf(m, "# WARNING: FUNCTION TRACING IS CORRUPTED\n");

	seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");

}



static int s_show(struct seq_file *m, void *v)

{

	struct trace_iterator *iter = v;
@@ -2169,6 +2177,7 @@ static int s_show(struct seq_file *m, void *v) 
		if (iter->tr) {

			seq_printf(m, "# tracer: %s\n", iter->trace->name);

			seq_puts(m, "#\n");

			test_ftrace_alive(m);

		}

		if (iter->trace && iter->trace->print_header)

			iter->trace->print_header(m);
@@ -4613,6 +4622,12 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode) 


	tracing_off();



	/* Did function tracer already get disabled? */

	if (ftrace_is_dead()) {

		printk("# WARNING: FUNCTION TRACING IS CORRUPTED\n");

		printk("#          MAY BE MISSING FUNCTION EVENTS\n");

	}



	if (disable_tracing)

		ftrace_kill();

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -579,11 +579,13 @@ static inline int ftrace_trace_task(struct task_struct *task) 


	return test_tsk_trace_trace(task);

}

extern int ftrace_is_dead(void);

#else

static inline int ftrace_trace_task(struct task_struct *task)

{

	return 1;

}

static inline int ftrace_is_dead(void) { return 0; }

#endif



/*

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