Commit a2250634 authored Nov 18, 2008 by Heiko Carstens Committed by Ingo Molnar Nov 18, 2008

ftrace: preemptoff selftest not working



Impact: fix preemptoff and preemptirqsoff tracer self-tests

I was wondering why the preemptoff and preemptirqsoff tracer selftests
don't work on s390. After all its just that they get called from
non-preemptible context:

kernel_init() will execute all initcalls, however the first line in
kernel_init() is lock_kernel(), which causes the preempt_count to be
increased. Any later calls to add_preempt_count() (especially those
from the selftests) will therefore not result in a call to
trace_preempt_off() since the check below in add_preempt_count()
will be false:

        if (preempt_count() == val)
                trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));

Hence the trace buffer will be empty.

Fix this by releasing the BKL during the self-tests.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 1c80025a

kernel/trace/trace.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -532,6 +532,13 @@ int register_tracer(struct tracer *type)
		}

		#ifdef CONFIG_FTRACE_STARTUP_TEST
		/*
		* When this gets called we hold the BKL which means that preemption
		* is disabled. Various trace selftests however need to disable
		* and enable preemption for successful tests. So we drop the BKL here
		* and grab it after the tests again.
		*/
		unlock_kernel();
		if (type->selftest) {
		struct tracer *saved_tracer = current_trace;
		struct trace_array *tr = &global_trace;
		@@ -562,6 +569,7 @@ int register_tracer(struct tracer *type)
		}
		printk(KERN_CONT "PASSED\n");
		}
		lock_kernel();
		#endif

		type->next = trace_types;