Re: net: deadlock between ip_expire/sch_direct_xmit

[Dmitry Vyukov]

On Tue, Mar 14, 2017 at 3:56 PM, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> On Tue, Mar 14, 2017 at 7:46 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
>> I am confused. Lockdep has observed both of these stacks:
>>
>>        CPU0                    CPU1
>>        ----                    ----
>>   lock(&(&q->lock)->rlock);
>>                                lock(_xmit_ETHER#2);
>>                                lock(&(&q->lock)->rlock);
>>   lock(_xmit_ETHER#2);
>>
>>
>> So it somehow happened. Or what do you mean?
>>
>
> Lockdep said " possible circular locking dependency detected " .
> It is not an actual deadlock, but lockdep machinery firing.
>
> For a dead lock to happen, this would require that he ICMP message
> sent by ip_expire() is itself fragmented and reassembled.
> This cannot be, because ICMP messages are not candidates for
> fragmentation, but lockdep can not know that of course...


Ah, I see. Thanks.