linux-kernel - Re: [PATCH v1 4/7] iommu/vt-d: Remove unnecessary local variable initializations

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Message-ID: <63ae370c-2239-62c5-2378-98916608acc4@linux.intel.com>
Date:   Mon, 11 Feb 2019 09:55:24 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>, Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/7] iommu/vt-d: Remove unnecessary local variable
 initializations

Hi,

On 2/9/19 6:06 AM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> A local variable initialization is a hint that the variable will be used in
> an unusual way.  If the initialization is unnecessary, that hint becomes a
> distraction.
> 
> Remove unnecessary initializations.  No functional change intended.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>   drivers/iommu/intel-iommu.c |   27 +++++++++++++--------------
>   1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 81077803880f..2acd08c82cdc 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -865,7 +865,7 @@ static void free_context_table(struct intel_iommu *iommu)
>   static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain,
>   				      unsigned long pfn, int *target_level)
>   {
> -	struct dma_pte *parent, *pte = NULL;
> +	struct dma_pte *parent, *pte;
>   	int level = agaw_to_level(domain->agaw);
>   	int offset;
>   
> @@ -922,7 +922,7 @@ static struct dma_pte *dma_pfn_level_pte(struct dmar_domain *domain,
>   					 unsigned long pfn,
>   					 int level, int *large_page)
>   {
> -	struct dma_pte *parent, *pte = NULL;
> +	struct dma_pte *parent, *pte;
>   	int total = agaw_to_level(domain->agaw);
>   	int offset;
>   
> @@ -954,7 +954,7 @@ static void dma_pte_clear_range(struct dmar_domain *domain,
>   				unsigned long start_pfn,
>   				unsigned long last_pfn)
>   {
> -	unsigned int large_page = 1;
> +	unsigned int large_page;
>   	struct dma_pte *first_pte, *pte;
>   
>   	BUG_ON(!domain_pfn_supported(domain, start_pfn));
> @@ -1132,7 +1132,7 @@ static struct page *domain_unmap(struct dmar_domain *domain,
>   				 unsigned long start_pfn,
>   				 unsigned long last_pfn)
>   {
> -	struct page *freelist = NULL;
> +	struct page *freelist;

I am afraid this change might cause problem. "freelist" might go through
dma_pte_clear_level() without any touches.

Best regards,
Lu Baolu