linux-kernel - Re: [PATCH] MIPS: Fix DMA contiguous allocation

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Date:	Tue, 8 Dec 2015 15:12:49 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Qais Yousef <qais.yousef@...tec.com>, linux-mips@...ux-mips.org
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	ralf@...ux-mips.org, akpm@...ux-foundation.org,
	mgorman@...hsingularity.net
Subject: Re: [PATCH] MIPS: Fix DMA contiguous allocation

On 12/8/2015 1:18 PM, Qais Yousef wrote:

> Recent changes to how GFP_ATOMIC is defined seems to have broken the condition
> to use mips_alloc_from_contiguous() in mips_dma_alloc_coherent().
>
> I couldn't bottom out the exact change but I think it's this one
>
> d0164adc89f6 (mm, page_alloc: distinguish between being unable to sleep,
> unwilling to sleep and avoiding waking kswapd)
>
>  From what I see GFP_ATOMIC has multiple bits set and the check for !(gfp
> & GFP_ATOMIC) isn't enough. To verify if the flag is atomic we need to make
> sure that (gfp & GFP_ATOMIC) == GFP_ATOMIC to verify that all bits rquired to

    Required.

> satisfy GFP_ATOMIC condition are set.
>
> Signed-off-by: Qais Yousef <qais.yousef@...tec.com>
> ---
>   arch/mips/mm/dma-default.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
> index d8117be729a2..d6b8a1445a3a 100644
> --- a/arch/mips/mm/dma-default.c
> +++ b/arch/mips/mm/dma-default.c
> @@ -145,7 +145,7 @@ static void *mips_dma_alloc_coherent(struct device *dev, size_t size,
>
>   	gfp = massage_gfp_flags(dev, gfp);
>
> -	if (IS_ENABLED(CONFIG_DMA_CMA) && !(gfp & GFP_ATOMIC))
> +	if (IS_ENABLED(CONFIG_DMA_CMA) && ((gfp & GFP_ATOMIC) != GFP_ATOMIC))

    () around != not necessary.

[...]

MBR, Sergei

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