On Wed, 2005-10-26 at 18:52 -0700, john stultz wrote:
> On Wed, 2005-10-26 at 21:37 -0400, Steven Rostedt wrote:
> > On Wed, 2005-10-26 at 18:22 -0700, john stultz wrote:
> >
> > >
> > > I don't know if that would really fix it, because ideally you want to
> > > read the prev_mono_time at the same point you calculate the time inside
> > > the read lock'ed critical section.
> >
> > Ideally yes, but this is just for debugging, so as long as prev is read
> > before now, this should prevent false positives due to ordering.
>
> Ah, you're right, good point! I was being overly paranoid.
>
> So as long as the writing of the 64bit value is atomic (which it isn't,
> but that can be fixed) there shouldn't be ordering problems w/ your
> patch.
Turning off IRQs should be good enough.
>
> And sure enough, it seems to take care of the warnings on my box.
So I guess interrupts do call this. :-)
Thanks,
-- Steve
Here's a updated patch.
Index: linux-2.6.14-rc5-rt7/kernel/time/timeofday.c
===================================================================
--- linux-2.6.14-rc5-rt7.orig/kernel/time/timeofday.c 2005-10-26 16:57:03.000000000 -0400
+++ linux-2.6.14-rc5-rt7/kernel/time/timeofday.c 2005-10-26 22:10:32.000000000 -0400
@@ -232,6 +232,12 @@
unsigned long seq;
ktime_t prev, now;
nsec_t mc, prev_st, curr_st;
+ unsigned long flags;
+
+ raw_local_irq_save(flags);
+ prev = per_cpu(prev_mono_time, cpu);
+ prev_st = per_cpu(prev_system_time, cpu);
+ raw_local_irq_restore(flags);
/* atomically read __get_monotonic_clock_ns() */
do {
@@ -242,11 +248,7 @@
} while (read_seqretry(&system_time_lock, seq));
ns_to_timespec(ts, mc);
-
now = timespec_to_ktime(*ts);
- prev = per_cpu(prev_mono_time, cpu);
-
- prev_st = per_cpu(prev_system_time, cpu);
curr_st = system_time;
if (ktime_cmp(now, <, prev)) {
@@ -264,8 +266,12 @@
ktime_to_timespec(ts, prev);
return;
}
+
+ raw_local_irq_save(flags);
per_cpu(prev_mono_time, cpu) = now;
per_cpu(prev_system_time, cpu) = system_time;
+ raw_local_irq_restore(flags);
+
put_cpu();
}
-
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