Essentially, you can see logs like

KERCALL_ENTER
<preemption occurs while the kernel call is occurring, another thread 
runs, then eventually kernel call restarts>
KERCALL_ENTER
KERCALL_EXIT

ie you have an uneven number of kernel entries to exits.
> Hi,
>
> Can you please explain this in more details, from the system analysis toolkit user's guide:
>
> --- START
> Thread restarting:
>
> In order to achieve maximum responsiveness, much of the QNX Neutrino microkernel is fully preemptible. In some cases, 
this means that when a thread is interrupted in a kernel call, it won’t be able to restart exactly where it began. 
Instead, the kernel call will be restarted—it “rewinds” itself. The SAT tries to hide the spurious calls but may not 
succeed in suppressing them all. As a result, it’s possible to see several events generated from a specific thread that
 has been preempted. If this occurs, the last event is the actual one.
> --- END
>
> Thank you,
> Karim Mouline.
>
>
>
> _______________________________________________
>
> General
> http://community.qnx.com/sf/go/post78766

-- 
cburgess@qnx.com