[PATCH] MIPS: Fix DMA contiguous allocation

[PATCH] MIPS: Fix DMA contiguous allocation

[Qais Yousef]

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
satisfy GFP_ATOMIC condition are set.

Signed-off-by: Qais Yousef <qais.yousef@imgtec.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))
 		page = dma_alloc_from_contiguous(dev,
 					count, get_order(size));
 	if (!page)
-- 
2.1.0

Re: [PATCH] MIPS: Fix DMA contiguous allocation

[Sergei Shtylyov]

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@imgtec.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

Re: [PATCH] MIPS: Fix DMA contiguous allocation

[Andrew Morton]

On Tue, 8 Dec 2015 10:18:50 +0000 Qais Yousef <qais.yousef@imgtec.com> 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
> satisfy GFP_ATOMIC condition are set.
> 
> ...
>
> --- 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))
>  		page = dma_alloc_from_contiguous(dev,
>  					count, get_order(size));
>  	if (!page)

hm.  It seems that the code is asking "can I do a potentially-sleeping
memory allocation"?

The way to do that under the new regime is

	if (IS_ENABLED(CONFIG_DMA_CMA) && gfpflags_allow_blocking(gfp))

Mel, can you please confirm?

Re: [PATCH] MIPS: Fix DMA contiguous allocation

[Mel Gorman]

On Tue, Dec 08, 2015 at 02:19:39PM -0800, Andrew Morton wrote:
> On Tue, 8 Dec 2015 10:18:50 +0000 Qais Yousef <qais.yousef@imgtec.com> 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
> > satisfy GFP_ATOMIC condition are set.
> > 
> > ...
> >
> > --- 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))
> >  		page = dma_alloc_from_contiguous(dev,
> >  					count, get_order(size));
> >  	if (!page)
> 
> hm.  It seems that the code is asking "can I do a potentially-sleeping
> memory allocation"?
> 
> The way to do that under the new regime is
> 
> 	if (IS_ENABLED(CONFIG_DMA_CMA) && gfpflags_allow_blocking(gfp))
> 
> Mel, can you please confirm?

Yes, this is the correct way it should be checked. The full flags cover
watermark and kswapd treatment which potentially could be altered by
the caller.

-- 
Mel Gorman
SUSE Labs

Re: [PATCH] MIPS: Fix DMA contiguous allocation

[Qais Yousef]

On 12/09/2015 11:36 AM, Mel Gorman wrote:
> On Tue, Dec 08, 2015 at 02:19:39PM -0800, Andrew Morton wrote:
>> On Tue, 8 Dec 2015 10:18:50 +0000 Qais Yousef <qais.yousef@imgtec.com> wrote:
>>
>>> --- 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))
>>>   		page = dma_alloc_from_contiguous(dev,
>>>   					count, get_order(size));
>>>   	if (!page)
>> hm.  It seems that the code is asking "can I do a potentially-sleeping
>> memory allocation"?
>>
>> The way to do that under the new regime is
>>
>> 	if (IS_ENABLED(CONFIG_DMA_CMA) && gfpflags_allow_blocking(gfp))
>>
>> Mel, can you please confirm?
> Yes, this is the correct way it should be checked. The full flags cover
> watermark and kswapd treatment which potentially could be altered by
> the caller.
>

OK thanks both. I'll send a revised version with this change.

Thanks,
Qais