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KVM guest: prevent tracing recursion with kvmclock 

Prevent tracing of preempt_disable() in get_cpu_var() in
kvm_clock_read(). When CONFIG_DEBUG_PREEMPT is enabled,
preempt_disable/enable() are traced and this causes the function_graph
tracer to go into an infinite recursion. By open coding the
preempt_disable() around the get_cpu_var(), we can use the notrace
version which prevents preempt_disable/enable() from being traced and
prevents the recursion.

Based on a similar patch for Xen from Jeremy Fitzhardinge.

Tested-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Avi Kivity 2011-11-15 14:59:07 +02:00
parent bb75c627fb
commit 95ef1e5292
1 changed files with 3 additions and 2 deletions
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5
arch/x86/kernel/kvmclock.c
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@ -74,9 +74,10 @@ static cycle_t kvm_clock_read(void)
struct pvclock_vcpu_time_info *src;
cycle_t ret;
src = &get_cpu_var(hv_clock);
preempt_disable_notrace();
src = &__get_cpu_var(hv_clock);
ret = pvclock_clocksource_read(src);
put_cpu_var(hv_clock);
preempt_enable_notrace();
return ret;
}