From: Christian Borntraeger <borntraeger@de.ibm.com>
Date: Tue, 19 Aug 2014 14:45:56 +0000 (+0200)
Subject: KVM: avoid unnecessary synchronize_rcu
X-Git-Tag: firefly_0821_release~3680^2~36^2~16^2^2~48
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=7fdbe25673a0bcd4c38968ec2cd048a21f1fbb93;p=firefly-linux-kernel-4.4.55.git

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>
(cherry picked from commit 7103f60de8bed21a0ad5d15d2ad5b7a333dda201)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
---

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 50f947301fa7..aa5057e7a1b9 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();