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    SubjectRe: 2.6.13-rc6-rt9
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    On Fri, 2005-08-19 at 09:00 -0400, Steven Rostedt wrote:
    > On Fri, 2005-08-19 at 02:39 -0400, Steven Rostedt wrote:

    > I haven't thought of a good way yet to solve the race condition with
    > dependent sleeper. (Except by turning off CONFIG_WAKEUP_TIMING :-)
    >

    OK, I found one simple solution. The problem stems from max_mutex being
    grabbed. Since this uses the RT locks, and since tracing shouldn't
    really care about PI and all that, I switched this to a
    compat_semaphore, but only if CONFIG_WAKEUP_TIMING is set. This seems to
    get rid of this race condition that I have.

    I found more bugs, but for now this message is about this specific race.

    -- Steve

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

    Index: linux_realtime_ernie/kernel/latency.c
    ===================================================================
    --- linux_realtime_ernie/kernel/latency.c (revision 297)
    +++ linux_realtime_ernie/kernel/latency.c (working copy)
    @@ -102,7 +102,19 @@
    /*
    * Track maximum latencies and save the trace:
    */
    +#ifdef CONFIG_WAKEUP_TIMING
    +/*
    + * The WAKEUP_TIMING has a race condition, since
    + * trace_stop_sched_switched might be called with run queue locks held
    + * which eventually calls down_trylock.
    + * But the RT version of down_trylock grabs a bunch of locks that
    + * are used by rt_up. rt_up can call wake_up_process which
    + * eventually grabs a run queue lock.
    + */
    +static __cacheline_aligned_in_smp COMPAT_DECLARE_MUTEX(max_mutex);
    +#else
    static __cacheline_aligned_in_smp DECLARE_MUTEX(max_mutex);
    +#endif
    /*
    * Sequence count - we record it when starting a measurement and
    * skip the latency if the sequence has changed - some other section

    -
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