Re: [PATCH] scsi: Allow error handling timeout to be specified

[Baruch Even <baruch@ev-en.org>]

On Fri, May 10, 2013 at 11:18 PM, Hannes Reinecke <hare@suse.de> wrote:
> On 05/10/2013 07:51 PM, Baruch Even wrote:
>>
>> The error handling I have in mind (admittedly, not fully thought out)
>> should work for both FC and SAS. Currently the error recovery
>> progresses at the host level regardless of if the errors are on one
>> device or all of them, it also stops the IOs on all devices and LUNs.
>> It would be nice if that was taken into account. My ideas may be more
>> suitable to the environment I work in (enterprise storage devices
>> rather than hosts) but I believe the same approach would benefit the
>> hosts as well.
>>
>> It would be interesting to see what approach the new error handling will
>> take.
>>
> So, my general idea is this:
>
> 1) Send command aborts from scsi_times_out(). There is no requirement
>    on stopping I/O on the host simply because a single command times
>    out. And as scsi_times_out() is run from a separate thread anyway
>    we should be able to send ABORT TASK TMFs without a problem
> 2) Modify recovery sequence.
>    One of the major pitfalls of the current scsi_eh is that it
>    spills over onto unrelated LUNs for higher levels. So for the
>    new EH we should be using a sequence of
>    - ABORT TASK
>    - ABORT TASK SET
>    - (Terminate I_T nexus)
>    - (Host reset)
>    'Terminate I_T nexus' for FibreChannel is equivalent to a LOGO.
>    'Host reset' is the current host reset function.
> 3) Finegrained recovery setting.
>    There is no need to stop the entire host when doing a recovery;
>    it should be sufficient to stop I/O to the unit
>    (LUN, I_T nexus, host) when the error recovery is at the
>    respective level.

This looks great and much in line with what I'm thinking.

What about not going to the higher level if not everything at that
level had failed?
I mean that if at the target not all LUNs failed it will be quite
troublesome to other LUNs if I-T-Nexus is terminated and that at the
host level if there are still targets that are functioning it will
kill them too to reset the host.

Will this replace all of EH or just FC EH?

Baruch