Re: 2.6.14-rc4-rt7

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 2005-10-26 at 17:45 -0700, john stultz wrote:

> Ok, I've reproduced the issue. 
> 
> However, running a clock_gettime(CLOCK_MONOTONIC) inconsistency check
> results in no failures, but triggers this code in the kernel.
> 
> Looking at the code, these may be false positives. The bit that is
> complaining I believe Ingo added to get_monotonic_clock_ts() in
> kernel/time/timeofday.c.  However I don't see any locking that
> serializes the writes the prev in the same order as the
> get_monotonic_clock_ts is called.
> 
> I'm still digging and will send out some mail when I figure out whats
> wrong.

Hmm, I'm wondering if these are a false positive. Being a fully
preemptible kernel, we could be preempted between taking now and getting
prev, so the prev could be updated to a time after now and show a warp.

William and Rui, could you try this patch and see if you still get the
warnings.  Although I doubt this is really the problem, since I can't
see how it would cause clusters of these messages.

-- Steve

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 21:03:22.000000000 -0400
@@ -243,8 +243,8 @@
 
 	ns_to_timespec(ts, mc);
 
-	now = timespec_to_ktime(*ts);
 	prev = per_cpu(prev_mono_time, cpu);
+	now = timespec_to_ktime(*ts);
 
 	prev_st = per_cpu(prev_system_time, cpu);
 	curr_st = system_time;