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Subject: Re: [4.1.3-rt8] [report][cpuhotplug] BUG: spinlock bad magic on
 CPU#0, sh/137
To: Thomas Gleixner <tglx@linutronix.de>
References: <5617CE6D.9060800@ti.com>
 <alpine.DEB.2.11.1510120952560.6097@nanos>
CC: <linux-rt-users@vger.kernel.org>, David Miller <davem@davemloft.net>,
        <linux-kernel@vger.kernel.org>, Eric Dumazet <edumazet@google.com>,
        <netdev@vger.kernel.org>
From: Grygorii Strashko <grygorii.strashko@ti.com>
Message-ID: <561D4CA4.1010207@ti.com>
Date: Tue, 13 Oct 2015 21:25:40 +0300
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On 10/12/2015 11:16 AM, Thomas Gleixner wrote:
> On Fri, 9 Oct 2015, Grygorii Strashko wrote:
>> I can constantly see below error report with 4.1 RT-kernel on TI ARM dra7-evm
>> if I'm trying to unplug cpu1:
>>
>> [   57.737589] CPU1: shutdown
>> [   57.767537] BUG: spinlock bad magic on CPU#0, sh/137
>> [   57.767546]  lock: 0xee994730, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
> 
>> It looks like this backtrace was introduces by
>>
>> commit 91df05da13a6c6c358e71182e80f19f3c48d1615
>> net: Use skbufhead with raw lock
>>
>> I see the potential fix for this issue as below:
>>
>> index 4969c0d..f8c23de 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -7217,7 +7217,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
>>                  netif_rx_ni(skb);
>>                  input_queue_head_incr(oldsd);
>>          }
>> -       while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
>> +       while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
> 
> Your patch is white space damaged ....
> 
>>                  netif_rx_ni(skb);
>>                  input_queue_head_incr(oldsd);
>>          }
>>
>> input_pkt_queue is per-cpu queue and at this moment cpu is dead already,
>> so no one should touch it. But I'm not sure if my assumption is correct.
> 
> It is. Picking it up for the next release
> 

Thanks & Sorry. I've not expected this diff/hack to be applied as patch :(

-- 
regards,
-grygorii