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>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 396fda0..1689212 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -532,6 +532,13 @@
}
#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 @@
}
printk(KERN_CONT "PASSED\n");
}
+ lock_kernel();
#endif
type->next = trace_types;