linux-kernel - Re: [PATCH v2] iommu/iova: Use raw_cpu_ptr() instead of get_cpu

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Message-ID: <20171102173349.btd3b2xfklcfopmz@breakpoint.cc>
Date:   Thu, 2 Nov 2017 18:33:50 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, vinadhy@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/iova: Use raw_cpu_ptr() instead of
 get_cpu_ptr() for ->fq

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 Jörg?

> Cc: Joerg Roedel <joro@...tes.org>
> Cc: iommu@...ts.linux-foundation.org
> Reported-by: vinadhy@...il.com
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> On 2017-09-19 11:41:19 [+0200], Joerg Roedel wrote:
> > Hi Sebastian,
> Hi Jörg,
> 
> > 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.
> 
> v1…v2: 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