xen: use non-tracing preempt in xen_clocksource_read()
The tracing code used sched_clock() to get tracing timestamps, which
ends up calling xen_clocksource_read(). xen_clocksource_read() must
disable preemption, but if preemption tracing is enabled, this results
in infinite recursion.
I've only noticed this when boot-time tracing tests are enabled, but it
seems like a generic bug. It looks like it would also affect
kvm_clocksource_read().
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 5158c50..163b467 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -168,9 +168,10 @@
struct pvclock_vcpu_time_info *src;
cycle_t ret;
- src = &get_cpu_var(xen_vcpu)->time;
+ preempt_disable_notrace();
+ src = &__get_cpu_var(xen_vcpu)->time;
ret = pvclock_clocksource_read(src);
- put_cpu_var(xen_vcpu);
+ preempt_enable_notrace();
return ret;
}