linux-kernel - Re: [BUG] ide dma_timer

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Date:	Tue, 19 Jun 2007 20:10:25 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Linas Vepstas <linas@...tin.ibm.com>
Cc:	Stuart_Hayes@...l.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] ide dma_timer_expiry, then hard lockup

Hello.

Linas Vepstas wrote:

>>Stuart_Hayes@...l.com wrote:

>>>I think reading the IDE status register clears the interrupt in the IDE
>>>device, which might be causing the drive to think it's OK to generate
>>>another interrupt.

>>   This is not how IDE drives are supposed to act -- they won't proceed any 
>>further until "interrupt pending" condition is cleared, so these aren't 
>>supposed to be "stacked". This behavior however is not strictly specified 
>>by ATA standards IIRC, but I can't readily imagine such situaltion anyway 
>>unless tagged command queueing  (which is not supported by IDE core) and/or 
>>ATAPI command overlapping is in action...

> The problem only manifests during high io load; perhaps a missing mutex
> somewhere is blasting one thing too many out to the hard drive?

    Hm... not sure about this.

>>>This could either cause it to get stuck trying to
>>>service an interrupt that is never getting cleared as you suggested, or
>>>possibly when the next IRQ comes in the IDE IRQ handler gets stuck
>>>waiting for a spinlock that the code you're looking at already owns...?

>>   I could also imagine the HPT366 chip going mad and stalling the reads if 
>>the taskfile regs forever because of the incomplete DMA or even the drive 
>>going mad and not replying to I/O cycles with proper -IORDY handshake (i.e. 
>>holding it low all the time)...

> In my case, ctrl-alt-sysrq doesn't work, which makes it hard to debug.

> I'm thinking that trying to debug libata is a better idea, rather than
> investing time in ide, right?  Although at the moment, libata works even 
> less; see other email.

    Which makes me think this really is some *hardware* issue.

> --linas

MBR, Sergei
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