On Tue, Sep 17, 2013 at 10:47 AM, Levente Kurusa <levex@xxxxxxxxx> wrote:
> 2013-09-16 06:37 keltezéssel, Robert Hancock írta:
>
>> On Sat, Sep 14, 2013 at 9:09 AM, Levente Kurusa <levex@xxxxxxxxx> wrote:
>>>
>>> 2013-09-10 06:01 keltezéssel, Robert Hancock írta:
>>>
>>>> On 09/08/2013 12:35 AM, Levente Kurusa wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> I have been testing the Linux Kernel on a two year Toshiba NB100
>>>>> netbook of mine, however when I enabled SATA compatibility/legacy mode
>>>>> instead of AHCI mode in the BIOS, the kernel got stuck. I have pasted
>>>>> the relevant dmesg piece along with a patch that fixes it temporarily.
>>>>> What I suspect to be the cause is that the BIOS sets the device into
>>>>> IDE mode, but it will report it as a SATA device and hence libata tries
>>>>> to send ATA commands to it, which obviously makes it go bad. The patch
>>>>
>>>>
>>>>
>>>> No, the commands are the same whichever mode the controller is in. The
>>>> problem is presumably something else, like maybe some kind of interrupt
>>>> routing problem when the controller is in legacy mode.
>>>>
>>> Yes, I see now.
>>>
>>>
>>>>> fixes it, by adding a new field to ata_device called exce_cnt, which
>>>>> counts how many exceptions have occured. After three exceptions, it
>>>>> automatically disables the device. Also, please note this is my first
>>>>> ever patch for the kernel :-)
>>>>>
>>>>> The following dmesg is stuck in an infinite loop.
>>>>> dmesg:
>>>>> ata3: lost interrupt (Status 0x50)
>>>>> ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
>>>>> ata3.00: failed command: READ DMA
>>>>> ata3.00: cmd c8/00:08:00:00:00/00:00:00:00:00/e0 tag 0 dma 4096 in
>>>>> res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4
>>>>> (timeout)
>>>>> ata3.00: status: { DRDY }
>>>>> ata3: soft resetting link
>>>>> ata3.00: configured for UDMA/33 (no error)
>>>>> ata3.00: device reported invalid CHS sector 0
>>>>> ata3: EH complete
>>>>>
>>>>> Patch that fixes the infinite loop:
>>>>> diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
>>>>> index f9476fb..eeedf80 100644
>>>>> --- a/drivers/ata/libata-eh.c
>>>>> +++ b/drivers/ata/libata-eh.c
>>>>> @@ -2437,6 +2437,14 @@ static void ata_eh_link_report(struct ata_link
>>>>> *link)
>>>>> ehc->i.action, frozen, tries_buf);
>>>>> if (desc)
>>>>> ata_dev_err(ehc->i.dev, "%s\n", desc);
>>>>> + ehc->i.dev->exce_cnt ++;
>>>>> + ata_dev_warn(ehc->i.dev, "Number of exceptions: %d\n",
>>>>> ehc->i.dev->exce_cnt);
>>>>> + /**
>>>>> + * The device is failing terribly,
>>>>> + * disable it to prevent damage.
>>>>> + */
>>>>> + if(ehc->i.dev->exce_cnt > 2)
>>>>> + ata_dev_disable(ehc->i.dev);
>>>>> } else {
>>>>> ata_link_err(link, "exception Emask 0x%x "
>>>>> "SAct 0x%x SErr 0x%x action 0x%x%s%s\n",
>>>>> diff --git a/include/linux/libata.h b/include/linux/libata.h
>>>>> index eae7a05..fa52ee6 100644
>>>>> --- a/include/linux/libata.h
>>>>> +++ b/include/linux/libata.h
>>>>> @@ -660,7 +660,8 @@ struct ata_device {
>>>>> u8 devslp_timing[ATA_LOG_DEVSLP_SIZE];
>>>>>
>>>>> /* error history */
>>>>> - int spdn_cnt;
>>>>> + int spdn_cnt; /* Number of speed_downs */
>>>>> + int exce_cnt; /* Number of exceptions that
>>>>> happenned */
>>>>> /* ering is CLEAR_END, read comment above CLEAR_END */
>>>>> struct ata_ering ering;
>>>>> };
>>>>>
>>>>
>>>> This doesn't seem like a very good fix. It may prevent the apparent
>>>> infinite loop but will just prevent that device from functioning at all.
>>>> It would be better if we could figure out what was actually going wrong.
>>>>
>>>>
>>> I have tested the problem with three different computers, all switched
>>> to legacy/IDE/compatibility mode, and they didn't have this problem. Of
>>> course, they could have been set to AHCI mode, and there the kernel would
>>> boot normally. Feels strange, but so far I was only able to reproduce the
>>> problem with a Toshiba MK8052GSX. On the topic of my patch, I still don't
>>> see why a device which fails so terribly that it reports 3 exceptions
>>> shouldn't be disabled. Like in this case, it could cause infinite loops.
>>
>>
>> The problem is that this could happen in some cases when you wouldn't
>> want to disable the device, like an error that just happens
>> sporadically and works on retry, or a device you're trying to recover
>> data from.
>>
> What do you think if I edit the patch in a way, that when an operation
> successfully completes, it resets exce_cnt to zero. Might as well add a
> module_param, which can set the maximum value of exce_cnt, while having zero
> as an option to never disable the device. Please don't think me wrong, I
> don't want to force this patch, I just want to learn how all this works, and
> in the process try to make it better. :-)
That would be better, but I think you're still going to have an issue
with what magic number to pick to avoid disabling devices
inappropriately.
Conceptually, disabling the device doesn't really make sense anyway.
If someone in userspace wants to keep trying to read from that device,
why would you stop them because of some arbitrary judgement? The
kernel itself isn't "locked up" during this process, anything not
blocked on I/O to that device should be able to continue running, so
that process is only hurting itself. If the system fails to boot from
another device due to this, this would likely point out some kind of
problem in userspace or the distro boot process being overly
serialized.
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