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

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Date:	Tue, 25 Feb 2014 12:45:49 -0500
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Sander Eikelenboom <linux@...elenboom.it>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	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

On Thu, Feb 13, 2014 at 4:49 PM, Sander Eikelenboom
<linux@...elenboom.it> wrote:
>
> 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>

Is there a reason this isn't in Linus' tree yet?

josh
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