netdev - Re: [PATCH] r8169: Fix irq masking in rtl8169

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Date:	Wed, 18 Mar 2009 23:35:45 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	romieu@...zoreil.com
Cc:	fzu@...gehoertderstaat.de, netdev@...r.kernel.org, rjw@...k.pl
Subject: Re: [PATCH] r8169: Fix irq masking in rtl8169_interrupt()

From: Francois Romieu <romieu@...zoreil.com>
Date: Wed, 18 Mar 2009 23:36:29 +0100

> Karsten Wiese <fzu@...gehoertderstaat.de> :
> > Am Mittwoch 18 März 2009 schrieb Francois Romieu:
> [...]
> > > If netif_rx_schedule fails after napi is enabled, there is a
> > > racing poll thread to care for the transfer.
> > > 
> > > Stated differently the bug is noticeable because napi_enable() 
> > > should be called before request_irq() in rtl8169_open, right ?
> > 
> > Propably yes. That would mean the first interrupt is received before
> > rtl_hw_start() is called in rtl8169_open. The source of that
> > interrupt would be something else then?
> 
> All we need is thus a shared interrupt racing on a different CPU
> with rtl8169_open and some IO versus memory reordering so that
> the hardware is started and a change in the status register can
> be seen in the IRQ handler before napi_enable/NAPI_STATE_SCHED
> escapes from the CPU where rtl8169_open is running...
> 
> It does not look like a credible explanation. :o/

Agreed, looking at how this part of the driver works I can't
see how this condition can arise either.
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