linux-kernel - Re: [PATCH v4 08/11] KVM: arm/arm64: vgic-its: new helper functions to free the caches

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Date:   Wed, 18 Oct 2017 00:24:25 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, peter.maydell@...aro.org,
        andre.przywara@....com, wanghaibin.wang@...wei.com,
        wu.wubin@...wei.com, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH v4 08/11] KVM: arm/arm64: vgic-its: new helper functions
 to free the caches

On Tue, Oct 17, 2017 at 09:10:06AM +0200, Eric Auger wrote:
> From: wanghaibin <wanghaibin.wang@...wei.com>
> 
> We create 2 new functions that frees the device and
> collection lists. this is currently called by vgic_its_destroy()
> and we will add other callers in subsequent patches.

See my previous comments about language issues in this paragraph.

> 
> We also remove the check on its->device_list.next as it looks
> unnecessary. Indeed, the device list always is initialized
> when vgic_its_destroy gets called: the kvm device is removed
> by kvm_destroy_devices() which loops on all the devices
> added to kvm->devices. kvm_ioctl_create_device() only adds
> the device to kvm_devices once the lists have been initialized
> (in vgic_create_its).
> 
> We also move vgic_its_free_device to prepare for new callers.
> 
> Signed-off-by: wanghaibin <wanghaibin.wang@...wei.com>
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> ---
> [Eric] removed its->device_list.next which is not needed as
> pointed out by Wanghaibin. Reword the commit message
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 76 ++++++++++++++++++++++++--------------------
>  1 file changed, 41 insertions(+), 35 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 1c3e83f..f3f0026f 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -611,6 +611,45 @@ static void its_free_ite(struct kvm *kvm, struct its_ite *ite)
>  	kfree(ite);
>  }
>  
> +static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev)
> +{
> +	struct its_ite *ite, *tmp;
> +
> +	list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list)
> +		its_free_ite(kvm, ite);
> +	list_del(&dev->dev_list);
> +	kfree(dev);
> +}
> +
> +static void vgic_its_free_device_list(struct kvm *kvm, struct vgic_its *its)
> +{
> +	struct list_head *cur, *temp;
> +
> +	mutex_lock(&its->its_lock);
> +	list_for_each_safe(cur, temp, &its->device_list) {
> +		struct its_device *dev;
> +
> +		dev = list_entry(cur, struct its_device, dev_list);
> +		vgic_its_free_device(kvm, dev);
> +	}
> +	mutex_unlock(&its->its_lock);
> +}
> +
> +static void vgic_its_free_collection_list(struct kvm *kvm, struct vgic_its *its)
> +{
> +	struct list_head *cur, *temp;
> +
> +	list_for_each_safe(cur, temp, &its->collection_list) {
> +		struct its_collection *coll;
> +
> +		coll = list_entry(cur, struct its_collection, coll_list);
> +		list_del(cur);
> +		kfree(coll);
> +	}
> +	mutex_unlock(&its->its_lock);
> +}
> +
> +
>  static u64 its_cmd_mask_field(u64 *its_cmd, int word, int shift, int size)
>  {
>  	return (le64_to_cpu(its_cmd[word]) >> shift) & (BIT_ULL(size) - 1);
> @@ -1644,46 +1683,13 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
>  	return vgic_its_set_abi(its, NR_ITS_ABIS - 1);
>  }
>  
> -static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev)
> -{
> -	struct its_ite *ite, *tmp;
> -
> -	list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list)
> -		its_free_ite(kvm, ite);
> -	list_del(&dev->dev_list);
> -	kfree(dev);
> -}
> -
>  static void vgic_its_destroy(struct kvm_device *kvm_dev)
>  {
>  	struct kvm *kvm = kvm_dev->kvm;
>  	struct vgic_its *its = kvm_dev->private;
> -	struct list_head *cur, *temp;
> -
> -	/*
> -	 * We may end up here without the lists ever having been initialized.
> -	 * Check this and bail out early to avoid dereferencing a NULL pointer.
> -	 */
> -	if (!its->device_list.next)
> -		return;

Hmm, I feel like we managed to convince ourselves this was needed
before.

Andre, can you remember what your original rationale was here?

> -
> -	mutex_lock(&its->its_lock);
> -	list_for_each_safe(cur, temp, &its->device_list) {
> -		struct its_device *dev;
> -
> -		dev = list_entry(cur, struct its_device, dev_list);
> -		vgic_its_free_device(kvm, dev);
> -	}
> -
> -	list_for_each_safe(cur, temp, &its->collection_list) {
> -		struct its_collection *coll;
> -
> -		coll = list_entry(cur, struct its_collection, coll_list);
> -		list_del(cur);
> -		kfree(coll);
> -	}
> -	mutex_unlock(&its->its_lock);
>  
> +	vgic_its_free_device_list(kvm, its);
> +	vgic_its_free_collection_list(kvm, its);
>  	kfree(its);
>  }
>  
> -- 
> 2.5.5
> 

If we're really sure the original check was just a misunderstanding,
then this patch looks ok, given the fixes to the commit message.

Thanks,
-Christoffer