linux-kernel - Re: Hang during boot, bisected to commit 96d60303fd

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Date:	Fri, 4 Jun 2010 21:23:20 -0400
From:	Marc Dionne <marc.c.dionne@...il.com>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, garzik@...hat.com
Subject: Re: Hang during boot, bisected to commit 96d60303fd

On Thu, Jun 3, 2010 at 11:42 PM, Robert Hancock <hancockrwd@...il.com> wrote:
> On 06/03/2010 07:21 PM, Marc Dionne wrote:
>>
>> On Wed, Jun 2, 2010 at 10:00 PM, Matthew Garrett<mjg59@...f.ucam.org>
>>  wrote:
>>>
>>> On Wed, Jun 02, 2010 at 09:49:27PM -0400, Marc Dionne wrote:
>>>>
>>>>    Since somewhere early in the 2.6.35 merge window I've been seeing a
>>>> hang
>>>>    during boot.  The hang last roughly 30 seconds and is followed by
>>>> this:
>>>>
>>>>    ata4.00: exception Emask 0x0 SAct 0x1 SErr 0x0 action 0x6 frozen
>>>>    ata4.00: failed command: READ FPDMA QUEUED
>>>>    ata4.00: cmd 60/08:00:00:00:00/00:00:00:00:00/40 tag 0 ncq 4096 in
>>>>             res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>>>>    ata4.00: status: { DRDY }
>>>>    ata4: hard resetting link
>>>>    ahci_is_device_present: status is: 80
>>>>    ahci_is_device_present: status(2) is: 3
>>>>    ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
>>>>    ata4.00: configured for UDMA/133
>>>>    ata4.00: device reported invalid CHS sector 0
>>>>    ata4: EH complete
>>>>
>>>>    The system works normally once booted.  I had some time to do a
>>>> bisect
>>>>    today and it cleanly ended up pointing to this commit:
>>>>        96d60303fd: ahci: Turn off DMA engines when there's no device
>>>> attached
>>>>
>>>>    Reverting the commit makes the system boot cleanly as before.  System
>>>> has
>>>>    an Intel ICH10 based board, in AHCI mode, disk is an Intel X25M SSD.
>>>
>>> Hm, interesting. Jeff, any immediate ideas? I don't see this behaviour
>>> on my ICH10. Is there actually a device on ata4?
>>>
>>> --
>>> Matthew Garrett | mjg59@...f.ucam.org
>>
>> If it's helpful, attached are the dmesg output following a normal boot
>> and one with the hang.
>>
>> The only difference in the kernel used for those two boots is that the
>> return statement in ahci_start_engine following the call to
>> ahci_is_device_present is commented out for the normal boot case.
>> When the return statement is active, the 30 second hang occurs.
>
> Can you try and put a printk in where it's returning out of the
> ahci_start_engine method? I wonder if that's getting triggered somewhere
> unexpected..

Attached is a dmesg output with some printks added to show the status
when ahci_is_device_present causes ahci_start_engine to return early..

It looks to me like there's two passes through ahci_start_engine for
all ports, and during the first pass the port with the disk is showing
a status of 127, causing the function to return early and skipping the
start DMA part.  This seems to cause the hang later on.

I noticed that during this first pass all the print_id fields for the
ports are still set to -1, so as a test I made ahci_start_engine only
do the check for ahci_is_device_present if print_id != -1, and this
makes the system boot normally.

Marc

Download attachment "dmesg_ahci" of type "application/octet-stream" (51893 bytes)