Re: net: deadlock between ip_expire/sch_direct_xmit
From: Eric Dumazet
Date: Tue Mar 14 2017 - 10:57:16 EST
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...