linux-kernel - Re: [Patch v2 3/3] iommu: avoid taking iova_rbtree

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Date:   Fri, 29 Nov 2019 13:34:03 +0000
From:   John Garry <john.garry@...wei.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        <iommu@...ts.linux-foundation.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [Patch v2 3/3] iommu: avoid taking iova_rbtree_lock twice

On 29/11/2019 00:48, Cong Wang wrote:
> Both find_iova() and __free_iova() take iova_rbtree_lock,
> there is no reason to take and release it twice inside
> free_iova().
> 
> Fold them into the critical section by calling the unlock
> versions instead.

Since generally the iova would be non-NULL, this seems a reasonable 
change (which could be mentioned in the commit log)

John

> 
> Cc: Joerg Roedel <joro@...tes.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>   drivers/iommu/iova.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 184d4c0e20b5..f46f8f794678 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -390,10 +390,14 @@ EXPORT_SYMBOL_GPL(__free_iova);
>   void
>   free_iova(struct iova_domain *iovad, unsigned long pfn)
>   {
> -	struct iova *iova = find_iova(iovad, pfn);
> +	unsigned long flags;
> +	struct iova *iova;
>   
> +	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
> +	iova = private_find_iova(iovad, pfn);
>   	if (iova)
> -		__free_iova(iovad, iova);
> +		private_free_iova(iovad, iova);
> +	spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
>   
>   }
>   EXPORT_SYMBOL_GPL(free_iova);
>