Re: [net-next v13 06/11] net: mtip: Add mtip_switch_{rx|tx} functions to the L2 switch driver

[Lukasz Majewski <lukma@denx.de>]

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Hi Paolo,

> >  static void mtip_switch_tx(struct net_device *dev)
> >  {
> > +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> > +	struct switch_enet_private *fep = priv->fep;
> > +	unsigned short status;
> > +	struct sk_buff *skb;
> > +	unsigned long flags;
> > +	struct cbd_t *bdp;
> > +
> > +	spin_lock_irqsave(&fep->hw_lock, flags);  
> 
> This is called from napi (bh) context, and every other caller
> is/should be BH, too. You should use
> 
> 	spin_lock_bh()

I've double check the spin locking in the driver - I've also consult
the fec_main.c.

It looks like the mtip_switch_rx() and fec_enet_rx() are not using
explicit locks and rely on NAPI locking.

On the other hand - the fec_enet_tx (and corresponding MTIP variant)
use spin_lock(), not the _bh() variant.

> 
> Also please test your patches with CONFIG_LOCKDEP and
> CONFIG_DEBUG_SPINLOCK enabled, thet will help finding this king of
> issues.

This was enabled by default. By changing all locks to _bh() there were
deadlocks observed.

On the MTIP driver (due to this HW IP block) there are some locks which
must disable interrupts:

1. One is when mtip_adjust_link() is called - as it is the same for
both switch ports. Moreover, at some use cases it is required that the
switch IP block is reset.

2. The mtip_atable_dynamicms_learn_migration() - it changes the content
of dynamic switching table. IRQ from switch shall not be possible at
this time as it can be called from mtip_switch_rx() (from NAPI) and
from timer/kthread (at specified period).


To sum up:

I'm going to prepare the v14 with changes around the timer / kthread
running mtip_atable_dynamicms_learn_migration() and use time stamps
extracted from jiffies.

Locks will be optimized and following paradigm used with fec_main.c
driver.

> 
> /P


Best regards,

Lukasz Majewski

--

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