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    SubjectRe: ftrace: preemptoff selftest not working

    * Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

    > Hi Steven,
    >
    > 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.

    ah, indeed :-)

    side-effect of the removal of CONFIG_PREEMPT_BKL - these things were
    written before that and nobody noticed that the self-test stopped
    working for real.

    > The patch below makes the selftests working for me, since then they
    > run in preemptible context. But it is ugly and I'm not proposing it
    > for upstream ;)
    >
    > Just wanted to make you aware that there is a bug.

    indeed it's ugly. We could perhaps drop the BKL in the selftests?

    Ingo


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