virt: kvm: arm: vgic: Return failure code '-EBUSY' when mutex_trylock() fails

When mutex_trylock() fails, kvm_vgic_create() will not create 'vgic', so it need return failure code '-EBUSY' instead of '0' to let outside know about it.

Also simplify the code within kvm_vgic_create():

- kvm_for_each_vcpu() scanning once is enough for current case.

- Remove redundant variable 'vcpu_lock_idx'.

Signed-off-by Chen Gang <[email protected]>

---
 virt/kvm/arm/vgic.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

virt/kvm/arm/vgic.c +7 -8

index 3aaca49..5846725 100644
@@ -1933,7 +1933,7 @@ out:
 
 int kvm_vgic_create(struct kvm *kvm)
 {
-	int i, vcpu_lock_idx = -1, ret = 0;
+	int i, ret = 0;
 	struct kvm_vcpu *vcpu;
 
 	mutex_lock(&kvm->lock);

@@ -1949,13 +1949,12 @@ int kvm_vgic_create(struct kvm *kvm)
 	 * that no other VCPUs are run while we create the vgic.
 	 */
 	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (!mutex_trylock(&vcpu->mutex))
+		if (!mutex_trylock(&vcpu->mutex)) {
+			ret = -EBUSY;
 			goto out_unlock;
-		vcpu_lock_idx = i;
-	}
-
-	kvm_for_each_vcpu(i, vcpu, kvm) {
+		}
 		if (vcpu->arch.has_run_once) {
+			mutex_unlock(&vcpu->mutex);
 			ret = -EBUSY;
 			goto out_unlock;
 		}

@@ -1968,8 +1967,8 @@ int kvm_vgic_create(struct kvm *kvm)
 	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
 
 out_unlock:
-	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
-		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
+	while (i-- > 0) {
+		vcpu = kvm_get_vcpu(kvm, i);
 		mutex_unlock(&vcpu->mutex);
 	}
 

Signature · 1 line

1.9.3

Quoted 3 lines · Chen Gang

When mutex_trylock() fails, kvm_vgic_create() will not create 'vgic', so it need return failure code '-EBUSY' instead of '0' to let outside know about it.

I already sent a patch for the -EBUSY:
https://lists.cs.columbia.edu/pipermail/kvmarm/2014-November/011936.html

Quoted 6 lines

Also simplify the code within kvm_vgic_create():

- kvm_for_each_vcpu() scanning once is enough for current case.

- Remove redundant variable 'vcpu_lock_idx'.

I don't like using the iterator variable for this kind of thing because it can really break in languages where i is out-of-scope after the loop and it is too easy to reuse the iterator variable in later versions of the code.

That being said, the scanning once is slightly prettier I guess, but I'd rather not introduce the churn unless others (Marc) think this is a big win.

-Christoffer

Quoted 51 lines

Signed-off-by Chen Gang <[email protected]>

---
 virt/kvm/arm/vgic.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

virt/kvm/arm/vgic.c +7 -8

index 3aaca49..5846725 100644
@@ -1933,7 +1933,7 @@ out:
 
 int kvm_vgic_create(struct kvm *kvm)
 {
-	int i, vcpu_lock_idx = -1, ret = 0;
+	int i, ret = 0;
 	struct kvm_vcpu *vcpu;
 
 	mutex_lock(&kvm->lock);

@@ -1949,13 +1949,12 @@ int kvm_vgic_create(struct kvm *kvm)
 	 * that no other VCPUs are run while we create the vgic.
 	 */
 	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (!mutex_trylock(&vcpu->mutex))
+		if (!mutex_trylock(&vcpu->mutex)) {
+			ret = -EBUSY;
 			goto out_unlock;
-		vcpu_lock_idx = i;
-	}
-
-	kvm_for_each_vcpu(i, vcpu, kvm) {
+		}
 		if (vcpu->arch.has_run_once) {
+			mutex_unlock(&vcpu->mutex);
 			ret = -EBUSY;
 			goto out_unlock;
 		}

@@ -1968,8 +1967,8 @@ int kvm_vgic_create(struct kvm *kvm)
 	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
 
 out_unlock:
-	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
-		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
+	while (i-- > 0) {
+		vcpu = kvm_get_vcpu(kvm, i);
 		mutex_unlock(&vcpu->mutex);
 	}
 

Signature · 1 line

1.9.3