Re: [PATCH v2] iommu/iova: Use raw_cpu_ptr() instead of get_cpu_ptr() for ->fq

From: Sebastian Andrzej Siewior
Date: Thu Nov 02 2017 - 13:33:58 EST


On 2017-09-21 17:21:40 [+0200], Sebastian Andrzej Siewior wrote:
> get_cpu_ptr() disabled preemption and returns the ->fq object of the
> current CPU. raw_cpu_ptr() does the same except that it not disable
> preemption which means the scheduler can move it to another CPU after it
> obtained the per-CPU object.
> In this case this is not bad because the data structure itself is
> protected with a spin_lock. This change shouldn't matter however on RT
> it does because the sleeping lock can't be accessed with disabled
> preemption.

Did this make to your tree JÃrg?

> Cc: Joerg Roedel <joro@xxxxxxxxxx>
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: vinadhy@xxxxxxxxx
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> On 2017-09-19 11:41:19 [+0200], Joerg Roedel wrote:
> > Hi Sebastian,
> Hi JÃrg,
>
> > I moved the flushing to driver/iommu/iova.c to share it with the Intel
> > IOMMU and possibly other drivers too, so this patch does no longer apply
> > to v4.14-rc1. Can you update the patch to these changes?
>
> Sure.
>
> v1âv2: move the change from amd_iommu.c to iova.c
>
> drivers/iommu/iova.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 33edfa794ae9..b30900025c62 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -570,7 +570,7 @@ void queue_iova(struct iova_domain *iovad,
> unsigned long pfn, unsigned long pages,
> unsigned long data)
> {
> - struct iova_fq *fq = get_cpu_ptr(iovad->fq);
> + struct iova_fq *fq = raw_cpu_ptr(iovad->fq);
> unsigned long flags;
> unsigned idx;
>
> @@ -600,8 +600,6 @@ void queue_iova(struct iova_domain *iovad,
> if (atomic_cmpxchg(&iovad->fq_timer_on, 0, 1) == 0)
> mod_timer(&iovad->fq_timer,
> jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT));
> -
> - put_cpu_ptr(iovad->fq);
> }
> EXPORT_SYMBOL_GPL(queue_iova);
>
> --
> 2.14.1
>

Sebastian