linux-kernel - [PATCH 3.19 024/177] KVM: s390: no need to hold the kvm->mutex for floating interrupts

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Message-Id: <20150502190120.741253335@linuxfoundation.org>
Date:	Sat,  2 May 2015 21:00:46 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Jens Freimann <jfrei@...ux.vnet.ibm.com>
Subject: [PATCH 3.19 024/177] KVM: s390: no need to hold the kvm->mutex for floating interrupts

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger@...ibm.com>

commit 69a8d456263849152826542c7cb0a164b90e68a8 upstream.

The kvm mutex was (probably) used to protect against cpu hotplug.
The current code no longer needs to protect against that, as we only
rely on CPU data structures that are guaranteed to be available
if we can access the CPU. (e.g. vcpu_create will put the cpu
in the array AFTER the cpu is ready).

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@...ibm.com>
Reviewed-by: Jens Freimann <jfrei@...ux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/s390/kvm/interrupt.c |    8 --------
 1 file changed, 8 deletions(-)

--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1131,7 +1131,6 @@ struct kvm_s390_interrupt_info *kvm_s390
 
 	if ((!schid && !cr6) || (schid && cr6))
 		return NULL;
-	mutex_lock(&kvm->lock);
 	fi = &kvm->arch.float_int;
 	spin_lock(&fi->lock);
 	inti = NULL;
@@ -1159,7 +1158,6 @@ struct kvm_s390_interrupt_info *kvm_s390
 	if (list_empty(&fi->list))
 		atomic_set(&fi->active, 0);
 	spin_unlock(&fi->lock);
-	mutex_unlock(&kvm->lock);
 	return inti;
 }
 
@@ -1172,7 +1170,6 @@ static int __inject_vm(struct kvm *kvm,
 	int sigcpu;
 	int rc = 0;
 
-	mutex_lock(&kvm->lock);
 	fi = &kvm->arch.float_int;
 	spin_lock(&fi->lock);
 	if (fi->irq_count >= KVM_S390_MAX_FLOAT_IRQS) {
@@ -1225,7 +1222,6 @@ static int __inject_vm(struct kvm *kvm,
 	kvm_s390_vcpu_wakeup(kvm_get_vcpu(kvm, sigcpu));
 unlock_fi:
 	spin_unlock(&fi->lock);
-	mutex_unlock(&kvm->lock);
 	return rc;
 }
 
@@ -1379,7 +1375,6 @@ void kvm_s390_clear_float_irqs(struct kv
 	struct kvm_s390_float_interrupt *fi;
 	struct kvm_s390_interrupt_info	*n, *inti = NULL;
 
-	mutex_lock(&kvm->lock);
 	fi = &kvm->arch.float_int;
 	spin_lock(&fi->lock);
 	list_for_each_entry_safe(inti, n, &fi->list, list) {
@@ -1389,7 +1384,6 @@ void kvm_s390_clear_float_irqs(struct kv
 	fi->irq_count = 0;
 	atomic_set(&fi->active, 0);
 	spin_unlock(&fi->lock);
-	mutex_unlock(&kvm->lock);
 }
 
 static inline int copy_irq_to_user(struct kvm_s390_interrupt_info *inti,
@@ -1429,7 +1423,6 @@ static int get_all_floating_irqs(struct
 	int ret = 0;
 	int n = 0;
 
-	mutex_lock(&kvm->lock);
 	fi = &kvm->arch.float_int;
 	spin_lock(&fi->lock);
 
@@ -1448,7 +1441,6 @@ static int get_all_floating_irqs(struct
 	}
 
 	spin_unlock(&fi->lock);
-	mutex_unlock(&kvm->lock);
 
 	return ret < 0 ? ret : n;
 }


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