netdev - 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 09:50:45 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Josh Boyer <jwboyer@...oraproject.org>
Cc:	Sander Eikelenboom <linux@...elenboom.it>,
	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 Tue, Feb 25, 2014 at 9:45 AM, Josh Boyer <jwboyer@...oraproject.org> wrote:
> 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?
>

It's in -mm and now -next, I expect it will go upstream with akpm's next sync.

--
Dan
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