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Commit 95ef1e52 authored by Avi Kivity's avatar Avi Kivity
Browse files

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: default avatarGleb Natapov <gleb@redhat.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent bb75c627

arch/x86/kernel/kvmclock.c

+3 −2
Original line number Diff line number Diff line
@@ -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;

}