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

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Message-ID: <20090318223629.GA2306@electric-eye.fr.zoreil.com>
Date:	Wed, 18 Mar 2009 23:36:29 +0100
From:	Francois Romieu <romieu@...zoreil.com>
To:	Karsten Wiese <fzu@...gehoertderstaat.de>
Cc:	netdev@...r.kernel.org, Rafael Wysocki <rjw@...k.pl>
Subject: Re: [PATCH] r8169: Fix irq masking in rtl8169_interrupt()

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/

-- 
Ueimor
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