Date:	Mon, 18 Mar 2013 10:29:30 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	christoph.paasch@...ouvain.be
CC:	Alexander Duyck <alexander.duyck@...il.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: Re: igb_poll - device driver failed to check map error

On 03/16/2013 04:07 AM, Christoph Paasch wrote:
> On Friday 15 March 2013 16:08:31 Alexander Duyck wrote:
>> On 03/15/2013 12:52 AM, Christoph Paasch wrote:
>>> On Thursday 14 March 2013 19:18:18 Alexander Duyck wrote:
>>>> On 03/12/2013 02:31 AM, Christoph Paasch wrote:
>>>>> Hello,
>>>>>
>>>>> I'm seeing a warning while booting my machine when DMA_API_DEBUG is set:
>>>>>
>>>>> [   36.402824] ------------[ cut here ]------------
>>>>> [   36.458070] WARNING: at
>>>>> /home/cpaasch/builder/net-next/lib/dma-debug.c:934
>>>>> check_unmap+0x648/0x702()
>>>>> [   36.567377] Hardware name: ProLiant DL165 G7
>>>>> [   36.618452] igb 0000:04:00.0: DMA-API: device driver failed to check
>>>>> map
>>>>> error[device address=0x0000000233d9b232] [size=154 bytes] [mapped as
>>>>> single] [   36.776640] Modules linked in:
>>>>> [   36.815446] Pid: 0, comm: swapper/7 Not tainted 3.9.0-rc1-mptcp+ #101
>>>>> [   36.892515] Call Trace:
>>>>> [   36.921745]  <IRQ>  [<ffffffff8102ad7f>]
>>>>> warn_slowpath_common+0x80/0x9a
>>>>> [   37.001023]  [<ffffffff8102ae2d>] warn_slowpath_fmt+0x41/0x43
>>>>> [   37.069771]  [<ffffffff811db17f>] check_unmap+0x648/0x702
>>>>> [   37.134363]  [<ffffffff811db3e9>] debug_dma_unmap_page+0x50/0x52
>>>>> [   37.206234]  [<ffffffff8136676a>] igb_poll+0x144/0xf7c
>>>>> [   37.267706]  [<ffffffff8104dd19>] ? sched_clock_cpu+0x46/0xd1
>>>>> [   37.336456]  [<ffffffff814458ce>] net_rx_action+0xa7/0x1d0
>>>>> [   37.402085]  [<ffffffff81030b65>] __do_softirq+0xb4/0x16f
>>>>> [   37.466673]  [<ffffffff81030c90>] irq_exit+0x40/0x87
>>>>> [   37.526067]  [<ffffffff81002db1>] do_IRQ+0x98/0xaf
>>>>> [   37.583378]  [<ffffffff815210aa>] common_interrupt+0x6a/0x6a
>>>>> [   37.651086]  <EOI>  [<ffffffff8105d4be>] ?
>>>>> __tick_nohz_idle_enter+0x116/0x31f
>>>>> [   37.736595]  [<ffffffff81008a04>] ? default_idle+0x24/0x39
>>>>> [   37.802224]  [<ffffffff81008c62>] cpu_idle+0x68/0xa4
>>>>> [   37.861616]  [<ffffffff81519f78>] start_secondary+0x1a9/0x1ad
>>>>> [   37.930364] ---[ end trace 01b5bb0fd75a464c ]---
>>>>>
>>>>>
>>>>> It happens shortly after mounting the NFS-root filesystem.
>>>>>
>>>>> I tried to understand what is going on, but I am now at my wit's end.
>>>>>
>>>>> By adding some print-statements, here is what I found out (not sure if
>>>>> this is anyhow helpful):
>>>>>
>>>>> The difference between tx_buffer->time_stamp and the current 'jiffies'
>>>>> is
>>>>> up to 2000 jiffies (HZ==1000) at the first time the above warning
>>>>> happens
>>>>> (this seems too much for me). From then on, I see my print 3-4 times
>>>>> appear but without such a big difference between the timestamps
>>>>> (difference around 1 and 2 jiffies).
>>>>>
>>>>> Some other stuff, I printed:
>>>>> tx_buffer->skb: ffff880235054c80
>>>>> tx_buffer->bytecount: 154
>>>>> tx_buffer->gso_segs: 1
>>>>> tx_buffer->protocol: 8
>>>>> tx_buffer->tx_flags 0x20
>>>>>
>>>>>
>>>>> One last thing:
>>>>> Am I right that after each call to dma_map_single/page a call to
>>>>> dma_mapping_error is needed? If that's the case, I have some patches
>>>>> that
>>>>> add this statement at missing places in the e1000, e1000e and ixgb
>>>>> driver. But these patches do not fix my above problem.
>>>>>
>>>>>
>>>>> Thanks for your help,
>>>>> Christoph
>>>> Christoph,
>>>>
>>>> One thing that might be useful would be to reproduce this with a
>>>> standard 3.9-rc kernel instead of one using the multipath TCP patches.
>>>> This will help us to verify that the issue is reproducible with a stock
>>>> kernel and is not related to any ongoing work you may have only in your
>>>> tree.
>>> Hello,
>>>
>>> this is on a clean net-next kernel without any MPTCP-code.
>>>
>>> I bisected it down to  787314c35fbb (Merge tag 'iommu-updates-v3.8' of
>>> git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu), which simply
>>> introduces the debug_dma_mapping_error-checks.
>>>
>>> Am I right with the missing calls to dma_mapping_error in e1000, e1000e
>>> and
>>> ixgb?
>>>
>>> Cheers,
>>> Christoph
>> Christoph,
>>
>> The cause of this issues you are seeing may be due to the fact that the
>> buffer triggering the error is being reused.  I was able to reproduce
>> this issue occasionally with pktgen if I cloned the skb.  What may be
>> happening is that the buffer is being mapped in the transmit path on one
>> CPU while on another CPU the buffer is being cleaned.  Since the output
>> of each mapping is the physical address there is nothing to make each
>> mapping unique and I suspect this is resulting in false hits.
>>
>> You should be able to verify this if you were to check the skb->users
>> count as well as the dataref value in the skb_shared_info.  I suspect
>> either the users count of the dataref will be greater than 1.
> Both, users and dataref, are equal to 1. Before the call to dev_kfree_skb_any 
> and after dma_unmap_single fails.
>
>> You might also try testing the patch below to see if it has any effect.
>>  All it does is reorder the free and the unmap so that the buffer is not
>> freed for reuse until after we have checked it in the unmap path.
> I tested your patch, and it fixes my issue. Feel free to add a "Tested-by" to 
> the official patch.
>
>
> Cheers,
> Christoph

I'm not going to submit that as a fix since it doesn't resolve the
underlying issue and I still see problems when I do the pktgen test.

I'll try to submit a patch for the DMA debug API later today to resolve
the issue.  Basically what needs to happen is that we need to step
through and make it so that we tag each instance of the mapping
correctly instead of only tagging the first instance in the bucket.

Thanks,

Alex
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