On Wed, Nov 29, 2017 at 11:38:23AM -0500, Serhii Popovych wrote:
> Replace ->prepare_done flag functionality with special handling
> of -EBUSY in ->error as indicator that allocation work is running.
>
> Besides cosmetics this reduces size of struct kvm_resize_hpt by
> __alignof__(struct kvm_hpt_info) and saves few bytes of code.
>
> While there correct comment in struct kvm_resize_hpt about locking
> used to protect access to certain fields.
>
> Assert with BUG_ON() in case of HPT allocation thread work runs
> more than once for resize request or resize_hpt_allocate()
> returns -EBUSY that is treated specially.
>
> Change comparison against zero to make checkpatch.pl happy.
>
> Signed-off-by: Serhii Popovych <spopovyc@xxxxxxxxxx>
Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 42 ++++++++++++++++++++++---------------
> 1 file changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 235319c..0534aab 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -65,11 +65,17 @@ struct kvm_resize_hpt {
> u32 order;
>
> /* These fields protected by kvm->lock */
> +
> + /* Possible values and their usage:
> + * <0 an error occurred during allocation,
> + * -EBUSY allocation is in the progress,
> + * 0 allocation made successfuly.
> + */
> int error;
> - bool prepare_done;
>
> - /* Private to the work thread, until prepare_done is true,
> - * then protected by kvm->resize_hpt_sem */
> + /* Private to the work thread, until error != -EBUSY,
> + * then protected by kvm->lock.
> + */
> struct kvm_hpt_info hpt;
> };
>
> @@ -1432,15 +1438,21 @@ static void resize_hpt_prepare_work(struct work_struct *work)
> struct kvm *kvm = resize->kvm;
> int err;
>
> + BUG_ON(resize->error != -EBUSY);
> +
> resize_hpt_debug(resize, "resize_hpt_prepare_work(): order = %d\n",
> resize->order);
>
> err = resize_hpt_allocate(resize);
>
> + /* We have strict assumption about -EBUSY
> + * when preparing for HPT resize.
> + */
> + BUG_ON(err == -EBUSY);
> +
> mutex_lock(&kvm->lock);
>
> resize->error = err;
> - resize->prepare_done = true;
>
> mutex_unlock(&kvm->lock);
> }
> @@ -1465,14 +1477,12 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
>
> if (resize) {
> if (resize->order == shift) {
> - /* Suitable resize in progress */
> - if (resize->prepare_done) {
> - ret = resize->error;
> - if (ret != 0)
> - resize_hpt_release(kvm, resize);
> - } else {
> + /* Suitable resize in progress? */
> + ret = resize->error;
> + if (ret == -EBUSY)
> ret = 100; /* estimated time in ms */
> - }
> + else if (ret)
> + resize_hpt_release(kvm, resize);
>
> goto out;
> }
> @@ -1492,6 +1502,8 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
> ret = -ENOMEM;
> goto out;
> }
> +
> + resize->error = -EBUSY;
> resize->order = shift;
> resize->kvm = kvm;
> INIT_WORK(&resize->work, resize_hpt_prepare_work);
> @@ -1546,16 +1558,12 @@ long kvm_vm_ioctl_resize_hpt_commit(struct kvm *kvm,
> if (!resize || (resize->order != shift))
> goto out;
>
> - ret = -EBUSY;
> - if (!resize->prepare_done)
> - goto out;
> -
> ret = resize->error;
> - if (ret != 0)
> + if (ret)
> goto out;
>
> ret = resize_hpt_rehash(resize);
> - if (ret != 0)
> + if (ret)
> goto out;
>
> resize_hpt_pivot(resize);
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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