linux-kernel - Re: 3.14-mw regression: rtl8169 WARNING: DMA-API: exceeded 7 overlapping mappings of pfn 55ebe

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Date:	Thu, 13 Feb 2014 22:49:22 +0100
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Dan Williams <dan.j.williams@...el.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Francois Romieu <romieu@...zoreil.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: 3.14-mw regression: rtl8169 WARNING: DMA-API: exceeded 7 overlapping mappings of pfn 55ebe


Thursday, February 13, 2014, 9:14:47 PM, you wrote:

> On Tue, 2014-02-11 at 20:17 -0800, Eric Dumazet wrote:
>> On Tue, 2014-02-11 at 18:07 -0800, Dan Williams wrote:
>> 
>> > The overlap granularity is too large.  Multiple dma_map_single
>> > mappings are allowed to a given page as long as they don't collide on
>> > the same cache line.
>> > 
>> 
>> I am not sure why you try number of mappings of a page.
>> 
>> Try launching 100 concurrent netperf -t TCP_SENFILE
>> 
>> Same page might be mapped more than 100 times, more than 10000 times in
>> some cases.

> Thanks for that test case.

> I updated the fix patch with the following.

> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> index 42b12740940b..611010df1e9c 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -513,6 +513,13 @@ static int active_cln_insert(struct dma_debug_entry *entry)
>         unsigned long flags;
>         int rc;
>  
> +       /* If the device is not writing memory then we don't have any
> +        * concerns about the cpu consuming stale data.  This mitigates
> +        * legitimate usages of overlapping mappings.
> +        */
+       if (entry->>direction == DMA_TO_DEVICE)
> +               return 0;
> +
>         spin_lock_irqsave(&radix_lock, flags);
>         rc = radix_tree_insert(&dma_active_cacheline, to_cln(entry), entry);
>         if (rc == -EEXIST)
> @@ -526,6 +533,10 @@ static void active_cln_remove(struct dma_debug_entry *entry)
>  {
>         unsigned long flags;
>  
> +       /* ...mirror the insert case */
+       if (entry->>direction == DMA_TO_DEVICE)
> +               return;
> +
>         spin_lock_irqsave(&radix_lock, flags);
>         /* since we are counting overlaps the final put of the
>          * cacheline will occur when the overlap count is 0.


> Sander, barring a negative test result from you I'll send the attached
> patch to Andrew.

Hi Dan,

That seems to effectively suppress the warning, thanks and:

Tested-by; Sander Eikelenboom <linux@...elenboom.it>

--
Sander

> --
> Dan


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