linux-kernel - Re: [PATCH 2/2] sata_sil: disable DMA engine in ->freeze

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Date:	Wed, 08 Apr 2009 13:40:39 -0700
From:	Tejun Heo <htejun@...il.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Dustin Harrison <d.harrison@...us.com>,
	Sagar Borikar <sagar.borikar@...il.com>,
	linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 2/2] sata_sil: disable DMA engine in ->freeze

Hello,

Jeff Garzik wrote:
>> Thanks for updating the patch Jeff.  I see you spotted the reason why
>> I didn't put the code into sil_freeze.  I tested your patch and it
>> prevented the kernel panic.  I now get the following output, which
>> seems to be correct to me.
>>
>> WARNING: at drivers/ata/libata-core.c:5209 ata_qc_complete()
> 
> hum, my patch would indeed trigger this WARN_ON_ONCE() in
> ata_qc_complete():
> 
>         if (ap->ops->error_handler) {
>                 struct ata_device *dev = qc->dev;
>                 struct ata_eh_info *ehi = &dev->link->eh_info;
> 
>                 WARN_ON_ONCE(ap->pflags & ATA_PFLAG_FROZEN);
> 
> Tejun, was that WARN_ON() originally added to detect spurious callers?
> Or, completions after the EH started?
> 
> AFAICS, libata still owns the qc's at this point, so it should not be a
> problem to complete them when the port is frozen.

Ah... that one.  The WARN_ON_ONCE() was added because I was worried
that LLD interrupt handler might get activated after the port is
frozen and try to complete the commands which now belong to EH.  Given
that ata_qc_from_tag() returns NULL for any commands which get already
marked failed, it's a bit paranoid.  Well, I was a bit paranoid when
adding new EH the first time, so...

Removing it should be fine at this point, I think, but I'm away from
my toys so testing is a bit difficult, so please test the path which
triggered the WARN_ON_ONCE() works fine (it should) before removing
it.

Thanks.

-- 
tejun
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