netdev - Re: [PATCH resend] Renesas Ethernet AVB driver

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Message-ID: <552C48F7.5030901@gmx.de>
Date:	Tue, 14 Apr 2015 00:53:43 +0200
From:	Lino Sanfilippo <LinoSanfilippo@....de>
To:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
CC:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, devicetree@...r.kernel.org,
	galak@...eaurora.org, netdev@...r.kernel.org,
	linux-sh@...r.kernel.org
Subject: Re: [PATCH resend] Renesas Ethernet AVB driver

On 14.04.2015 00:31, Ben Hutchings wrote:

>> >> This driver looks somewhat similar to sh-eth, but lacks some of the
>> >> recent bug fixes made to that.  At least commit 283e38db65e7 ("sh_eth:
>> >> Fix serialisation of interrupt disable with interrupt & NAPI handler")
>> >> appears to be applicable, but there are probably others.
>> > 
>> >     I suspect this issue applies to many drivers...
>> >     I couldn't reproduce the bug that patch was fixing, so left this fix out 
>> > for the time being. Others cases were fixed (if applicable).
>> 
>> Maybe its just harder to trigger but it indeed looks similar to what Ben
>> has fixed for sh-eth. I wonder if that shutdown flag in the fix is
>> really needed though. IMHO it should be save if we simply call
>> napi_disable first, then disable irqs on hardware and finally
>> synchronize_irq...
> 
> In sh_eth: if we call napi_disable() first, EESR_RX_CHECK can still be
> set and nothing will clear it.  If only one CPU is online this can hard
> hang the system.  Please trust that I did consider and rule out the
> simpler approaches first.
> 

The idea was to check the return value from napi_schedule_prep() and in
case it returns "false" use this as an indication for a shutdown. In
case of sh_eth this would be sh_eth_write(ndev, 0, EESIPR) for example.

Lino


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