KVM: avoid unnecessary synchronize_rcu

We dont have to wait for a grace period if there is no oldpid that
we are going to free. putpid also checks for NULL, so this patch
only fences synchronize_rcu.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 33712fb26eb1..39b16035386f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -129,7 +129,8 @@ int vcpu_load(struct kvm_vcpu *vcpu)
                 struct pid *oldpid = vcpu->pid;
                 struct pid *newpid = get_task_pid(current, PIDTYPE_PID);
                 rcu_assign_pointer(vcpu->pid, newpid);
-                synchronize_rcu();
+                if (oldpid)
+                        synchronize_rcu();
                 put_pid(oldpid);
         }
         cpu = get_cpu();