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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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