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KVM: x86: fix deadlock in clock-in-progress request handling 

There is a deadlock in pvclock handling:

cpu0:                                               cpu1:
kvm_gen_update_masterclock()
                                              kvm_guest_time_update()
 spin_lock(pvclock_gtod_sync_lock)
                                               local_irq_save(flags)

spin_lock(pvclock_gtod_sync_lock)

 kvm_make_mclock_inprogress_request(kvm)
  make_all_cpus_request()
   smp_call_function_many()

Now if smp_call_function_many() called by cpu0 tries to call function on
cpu1 there will be a deadlock.

Fix by moving pvclock_gtod_sync_lock protected section outside irq
disabled section.

Analyzed by Gleb Natapov <gleb@redhat.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Reported-and-Tested-by: Yongjie Ren <yongjie.ren@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Marcelo Tosatti 2013-03-18 13:54:32 -03:00
parent f445f11eb2
commit c09664bb44
1 changed files with 9 additions and 9 deletions
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18
arch/x86/kvm/x86.c
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@ -1416,15 +1416,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
kernel_ns = 0;
host_tsc = 0;
/* Keep irq disabled to prevent changes to the clock */
local_irq_save(flags);
this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
if (unlikely(this_tsc_khz == 0)) {
local_irq_restore(flags);
kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
return 1;
}
/*
* If the host uses TSC clock, then passthrough TSC as stable
* to the guest.
@ -1436,6 +1427,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
kernel_ns = ka->master_kernel_ns;
}
spin_unlock(&ka->pvclock_gtod_sync_lock);
/* Keep irq disabled to prevent changes to the clock */
local_irq_save(flags);
this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
if (unlikely(this_tsc_khz == 0)) {
local_irq_restore(flags);
kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
return 1;
}
if (!use_master_clock) {
host_tsc = native_read_tsc();
kernel_ns = get_kernel_ns();