Re: [RFC] Re: Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses.

[Lino Sanfilippo]

Hi,

On 07.12.2016 13:31, Pavel Machek wrote:
> On Fri 2016-12-02 15:05:21, Lino Sanfilippo wrote:
> > Hi,
> >
> >
> > > There's nothing that protect stmmac_poll() from running concurently
> > > with stmmac_dma_interrupt(), right?
> >
> > could it be that there is also another issue concerned locking?:
> > The tx completion handler takes the xmit_lock in case that the
> > netif_queue is stopped. This is AFAICS unnecessary, since both
> > xmit and completion handler are already synchronized by the private
> > tx lock. But it is IMHO also dangerous:
> >
> > In the xmit handler we have the locking order
> > 1. xmit_lock
> > 2. private tx lock
> >
> > while in the completion handler its the reverse:
> >
> > 1. private tx lock
> > 2. xmit lock.
> >
> > Do I miss something?
>
> No, it seems you are right. Something like this?
>
> Hmm. And can priv->tx_lock be removed, as we already rely on
> netif_tx_lock?

David wanted indeed the private lock to be removed completely. See
this thread.

https://marc.info/?l=linux-netdev&m=148072001900620&w=2

If you can wait a bit, I already have patches prepared to fix this issue in both
drivers. I want to send them as soon as I am at home (a few hours).

Regards,
Lino