netdev - Re: [PATCH] macb: Add support of the netpoll API

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Date:	Thu, 16 Apr 2009 12:31:02 +0200
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	netdev@...r.kernel.org,
	Michael Opdenacker <michael@...e-electrons.com>
Subject: Re: [PATCH] macb: Add support of the netpoll API

Thomas Petazzoni wrote:
> Le Thu, 16 Apr 2009 11:07:53 +0200,
> Haavard Skinnemoen <haavard.skinnemoen@...el.com> a écrit :
> 
> > Hmm...is this safe? What if printk() is called from the macb interrupt
> > handler?  
> 
> I'm not sure, but that strategy is used in most drivers supporting the
> netpoll API (3c509.c, 8139cp.c, 8139too.c, b44.c, bfin_mac.c,
> bnx2x_main.c, etc.). It also seems to be the way suggested by netpoll
> author, http://oss.sgi.com/archives/netdev/2003-10/msg00800.html.
> 
> disable_irq() only disables the macb IRQ line. Is that an issue for
> printk() execution ?

I'm worried about this potential deadlock:
  macb_interrupt()
  calls printk()
  calls macb_poll_controller()
  calls disable_irq()
  calls synchronize_irq()
  waits until macb_interrupt() returns, which will never happen

So I think it's safer to just use local_irq_save(). The interrupt
handler shouldn't run for long anyway since it uses NAPI for RX
processing, and it probably ought to use NAPI for TX processing too,
eventually.

Haavard
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