Re: net: deadlock between ip_expire/sch_direct_xmit

[Eric Dumazet]

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...