Messages in this thread Patch in this message | | | Date | Mon, 16 Jan 2012 10:44:42 -0800 | From | Greg KH <> | Subject | [15/48] KVM guest: prevent tracing recursion with kvmclock |
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3.1-stable review patch. If anyone has any objections, please let me know.
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From: Avi Kivity <avi@redhat.com>
(cherry picked from commit 95ef1e52922cf75b1ea2eae54ef886f2cc47eecb)
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> --- arch/x86/kernel/kvmclock.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -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; }
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