Messages in this thread Patch in this message | | | Subject | Re: 2.6.13-rc6-rt9 | From | Steven Rostedt <> | Date | Fri, 19 Aug 2005 11:36:26 -0400 |
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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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