On Tue, Mar 14, 2017 at 7:56 AM, Eric Dumazet <eduma...@google.com> wrote:
> On Tue, Mar 14, 2017 at 7:46 AM, Dmitry Vyukov <dvyu...@google.com> 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...
It doesn't have to be ICMP, as long as get the same hash for
the inet_frag_queue, we will need to take the same lock and
deadlock will happen.
hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
So it is really up to this hash function.
