linux-kernel - Re: [git patches] libata updates for 2.6.34

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Date:	Thu, 11 Mar 2010 19:16:13 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	linux-ide@...r.kernel.org
CC:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [git patches] libata updates for 2.6.34

On 03/09/2010 11:26 PM, Tejun Heo wrote:
> Hello, Linus, Jeff.
>
> On 03/10/2010 07:12 AM, Jeff Garzik wrote:
>> Coincedentally, it looks like someone else just reported the same
>> problem, with 2.6.34-rc1.
>>
>> It definitely sounds like a race.  READ DMA is a DMA command as the name
>> implies, so that eliminates the possibility of polling-related paths in
>> ata_sff_interrupt (libata-sff.c).
>>
>> I'll flip some of my machines to the icky slow boring piix mode, rather
>> than sexy AHCI mode :) to see if I can reproduce.  I have had a feeling
>> that we needed a more sophisticated IRQ handling setup, this may be what
>> was needed.  Lost interrupt recovery should occur faster than 30 seconds
>> in any case, and should not require a hard reset if the hardware
>> functions just fine outside of the lost-interrupt / race that just
>> occurred.
>
> Yeap, there is a race condition with clearing which I don't think we
> can solve completely but with some modification I think we can at
> least cover known failure cases.
>
> For longer term, I don't think we can solve this by diddling with the
> SFF registers.  The interface is just way too ancient and horrid to
> build anything reliable on top of.  I'm planning on implementing
> smarter IRQ storm handling and stepped timeouts for ATA commands.

Another ata_piix report on l-i & lkml indicates that 2.6.33 is fine and 
libata timeouts occur on 2.6.34-rc1.

I was able to reproduce once, during disk stress.  I think I can do so 
again and hopefully verify a fix.

	Jeff



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