linux-kernel - Re: [PATCH 1/2] dma-mapping: Protect dma_addressing_limited against NULL dma

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Date:   Mon, 22 Jul 2019 17:46:00 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     eric.auger.pro@...il.com, m.szyprowski@...sung.com,
        robin.murphy@....com, mst@...hat.com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dma-mapping: Protect dma_addressing_limited against
 NULL dma_mask

Hi Christoph,

On 7/22/19 5:26 PM, Christoph Hellwig wrote:
>>  static inline bool dma_addressing_limited(struct device *dev)
>>  {
>> -	return min_not_zero(*dev->dma_mask, dev->bus_dma_mask) <
>> -		dma_get_required_mask(dev);
>> +	return WARN_ON_ONCE(!dev->dma_mask) ? false :
>> +		min_not_zero(*dev->dma_mask, dev->bus_dma_mask) <
>> +			dma_get_required_mask(dev);
> 
> This should really use a separate if statement, but I can fix that
> up when applying it.
> 
Just wondering why we don't use the dma_get_mask() accessor which
returns DMA_BIT_MASK(32) in case the dma_mask is not set.

Do you foresee any issue and would it still mandate to add dma_mask
checks on each call sites?

Thanks

Eric