netdev - Re: [BUG] net: stmmac: Panic observed in stmmac_napi_poll

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Date:   Mon, 17 May 2021 11:39:14 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Thierry Reding <treding@...dia.com>
Subject: Re: [BUG] net: stmmac: Panic observed in stmmac_napi_poll_rx()


On 14/05/2021 22:49, Michał Mirosław wrote:
> On Fri, May 14, 2021 at 03:24:58PM +0100, Jon Hunter wrote:
>> Hello!
>>
>> I have been looking into some random crashes that appear to stem from
>> the stmmac_napi_poll_rx() function. There are two different panics I
>> have observed which are ...
> [...]
>> The bug being triggered in skbuff.h is the following ...
>>
>>  void *skb_pull(struct sk_buff *skb, unsigned int len);
>>  static inline void *__skb_pull(struct sk_buff *skb, unsigned int len)
>>  {
>>          skb->len -= len;
>>          BUG_ON(skb->len < skb->data_len);
>>          return skb->data += len;
>>  }
>>
>> Looking into the above panic triggered in skbuff.h, when this occurs
>> I have noticed that the value of skb->data_len is unusually large ...
>>
>>  __skb_pull: len 1500 (14), data_len 4294967274
> [...]
> 
> The big value looks suspiciously similar to (unsigned)-EINVAL.

Yes it does and at first, I thought it was being set to -EINVAL.
However, from tracing the length variables I can see that this is not
the case.

>> I then added some traces to stmmac_napi_poll_rx() and
>> stmmac_rx_buf2_len() to trace the values of various various variables
>> and when the problem occurs I see ...
>>
>>  stmmac_napi_poll_rx: stmmac_rx: count 0, len 1518, buf1 66, buf2 1452
>>  stmmac_napi_poll_rx: stmmac_rx_buf2_len: len 66, plen 1518
>>  stmmac_napi_poll_rx: stmmac_rx: count 1, len 1518, buf1 66, buf2 1452
>>  stmmac_napi_poll_rx: stmmac_rx_buf2_len: len 66, plen 1536
>>  stmmac_napi_poll_rx: stmmac_rx: count 2, len 1602, buf1 66, buf2 1536
>>  stmmac_napi_poll_rx: stmmac_rx_buf2_len: len 1602, plen 1518
>>  stmmac_napi_poll_rx: stmmac_rx: count 2, len 1518, buf1 0, buf2 4294967212
>>  stmmac_napi_poll_rx: stmmac_rx: dma_buf_sz 1536, buf1 0, buf2 4294967212
> 
> And this one to (unsigned)-EILSEQ.

Yes but this simply comes from 1518-1602 = -84. So it is purely
coincidence.

Jon

-- 
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