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SubjectRe: ftrace: preemptoff selftest not working

* Steven Rostedt <rostedt@goodmis.org> wrote:

>
> On Tue, 18 Nov 2008, Heiko Carstens wrote:
> > >
> > > we can drop it in selected initcalls just fine. Its only role is
> > > old-style init functions racing with other async contexts of
> > > themselves.
> >
> > Something like below works fine for me...
> >
> > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
>
> Acked-by: Steven Rostedt <srostedt@redhat.com>

i've applied it in the form below to tip/tracing/ftrace, thanks guys!

Since it's only about the self-test, and since they have not been
working for a long time, i'm punting this to v2.6.29, not .28.

Ingo

------------->
From a22506347d038a66506c6f57e9b97104128e280d Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Tue, 18 Nov 2008 18:06:35 +0100
Subject: [PATCH] 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>
---
kernel/trace/trace.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
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 @@ 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;

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