netdev - Re: e1000_netpoll(): disable_irq() triggers might

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Message-ID: <alpine.DEB.2.11.1410292049350.5308@nanos>
Date:	Wed, 29 Oct 2014 20:53:37 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: e1000_netpoll(): disable_irq() triggers might_sleep() on
 linux-next

On Wed, 29 Oct 2014, Jeff Kirsher wrote:
> On Wed, 2014-10-29 at 20:36 +0100, Peter Zijlstra wrote:
> > On Wed, Oct 29, 2014 at 07:33:00PM +0100, Thomas Gleixner wrote:
> > > Yuck. No. You are just papering over the problem.
> > > 
> > > What happens if you add 'threadirqs' to the kernel command line? Or if
> > > the interrupt line is shared with a real threaded interrupt user?
> > > 
> > > The proper solution is to have a poll_lock for e1000 which serializes
> > > the hardware interrupt against netpoll instead of using
> > > disable/enable_irq().
> > > 
> > > In fact that's less expensive than the disable/enable_irq() dance and
> > > the chance of contention is pretty low. If done right it will be a
> > > NOOP for the CONFIG_NET_POLL_CONTROLLER=n case.
> > > 
> > 
> > OK a little something like so then I suppose.. But I suspect most all
> > the network drivers will need this and maybe more, disable_irq() is a
> > popular little thing and we 'just' changed semantics on them.
> 
> Thomas- if you are fine with Peter's patch, I can get this under
> testing.

I'm fine with it except for the comment part of disable_irq(), but
that does not matter :)

One nitpick: Instead of having the lock unconditionally, I'd make it
depend on CONFIG_NET_POLL_CONTROLLER.

#ifdef CONFIG_NET_POLL_CONTROLLER
static inline void netpoll_lock(struct e1000_adapter *adapter)
{
	spin_lock(&adapter->irq_lock);
}

static inline void netpoll_unlock(struct e1000_adapter *adapter)
{
	spin_unlock(&adapter->irq_lock);
}
#else
static inline void netpoll_lock(struct e1000_adapter *adapter) { }
static inline void netpoll_unlock(struct e1000_adapter *adapter) { }
#endif

and use that instead of the unconditional spin[un]lock() invocations.

But that's up to you.

Thanks,

	tglx

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