Commit 6e4eb9cb authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

ftrace: Add ftrace_test_recursion_trylock() helper function 

To make it easier for ftrace callbacks to have recursion protection, provide
a ftrace_test_recursion_trylock() and ftrace_test_recursion_unlock() helper
that tests for recursion.

Link: https://lkml.kernel.org/r/20201028115612.634927593@goodmis.org
Link: https://lkml.kernel.org/r/20201106023546.378584067@goodmis.org



Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 0264c8c9

include/linux/trace_recursion.h

+25 −0
Original line number Diff line number Diff line
@@ -183,5 +183,30 @@ static __always_inline void trace_clear_recursion(int bit) 
	current->trace_recursion = val;

}



/**

 * ftrace_test_recursion_trylock - tests for recursion in same context

 *

 * Use this for ftrace callbacks. This will detect if the function

 * tracing recursed in the same context (normal vs interrupt),

 *

 * Returns: -1 if a recursion happened.

 *           >= 0 if no recursion

 */

static __always_inline int ftrace_test_recursion_trylock(void)

{

	return trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);

}



/**

 * ftrace_test_recursion_unlock - called when function callback is complete

 * @bit: The return of a successful ftrace_test_recursion_trylock()

 *

 * This is used at the end of a ftrace callback.

 */

static __always_inline void ftrace_test_recursion_unlock(int bit)

{

	trace_clear_recursion(bit);

}



#endif /* CONFIG_TRACING */

#endif /* _LINUX_TRACE_RECURSION_H */

kernel/trace/trace_functions.c

+5 −7
Original line number Diff line number Diff line
@@ -141,22 +141,20 @@ function_trace_call(unsigned long ip, unsigned long parent_ip, 
	if (unlikely(!tr->function_enabled))

		return;



	bit = ftrace_test_recursion_trylock();

	if (bit < 0)

		return;



	pc = preempt_count();

	preempt_disable_notrace();



	bit = trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);

	if (bit < 0)

		goto out;



	cpu = smp_processor_id();

	data = per_cpu_ptr(tr->array_buffer.data, cpu);

	if (!atomic_read(&data->disabled)) {

		local_save_flags(flags);

		trace_function(tr, ip, parent_ip, flags, pc);

	}

	trace_clear_recursion(bit);



 out:

	ftrace_test_recursion_unlock(bit);

	preempt_enable_notrace();

}