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xen: use non-tracing preempt in xen_clocksource_read()

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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>
This commit is contained in:
Jeremy Fitzhardinge 2011-08-24 09:54:24 -07:00
parent fcb8ce5cfe
commit f1c39625d6
1 changed files with 3 additions and 2 deletions
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5
arch/x86/xen/time.c
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@ -168,9 +168,10 @@ cycle_t xen_clocksource_read(void)
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;
}