Re: tcm_loop and aborted TMRs

[Bodo Stroesser <bostroesser@gmail.com>]

On 12.11.22 22:46, michael.christie@oracle.com wrote:
> On 11/12/22 7:59 AM, Bodo Stroesser wrote:
>> Hello Mike, Maurizio,
>>
>> Even if we couldn't yet find a method to fix handling of aborted
>> TMRs in the core or in all fabric drivers, I still think that keeping
>> the parallel handling of TMRs would be fine.
>>
>> Tcmu offers a TMR notification mechanism to make userspace aware
>> of ABORT or RESET_LUN. So userspace can try to break cmd handling
>> and thus speed up TMR response. If we serialize TMR handling, then
>> the notifications are also serialized and thus lose some of their
>> power.
>>
>> But maybe I have a new (?) idea of how to fix handling of aborted
>> TMRs in fabric drivers:
>> 1) Modify core to not call target_put_sess_cmd, no matter whether
>>     SCF_ACK_REF is set.
>> 2) Modify fabric drivers to handle an aborted TMR just like a
>>     normal TMR response. This means, e.g. qla2xxx would send a
>>     normal response for the Abort. This exactly is what happens
>>     when serializing TMRs, because in that case despite of the
>>     RESET_LUN the core always calls queue_tm_rsp callback instead
>>     of aborted_task callback.
>>
>> So to initiators we would show the 'old' behavior, while internally
>> keeping the parallel processing of TMRs.
>>
>> If fabric driver maintainers don't like that approach, they can
>> change their drivers to correctly kill aborted TMRs.
>>
>> What do you think?
>>
> 
> I'm fine with doing it in parallel. However, the issue is we have real
> users hitting it now and we have to fix all the drivers because it's a
> regression. So if your idea is going take a while then we should revert
> now and then do your idea whenever it's ready.

I agree.

Even if my old patch fixes the issue for tcm_loop users, it does not
make sense to apply it, since the new idea would lead to reverting
parts of it. And with the patch we would still take the risk of users
running into trouble with fabrics other than tcm_loop.