linux-kernel - Re: [PATCH V2] scsi: libsas: Directly kick-off EH when ATA device fell off

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Date:   Mon, 19 Dec 2022 14:53:32 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     yangxingui <yangxingui@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, damien.lemoal@...nsource.wdc.com,
        linux-ide@...r.kernel.org, hare@...e.com, hch@....de
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, prime.zeng@...ilicon.com,
        kangfenglong@...wei.com
Subject: Re: [PATCH V2] scsi: libsas: Directly kick-off EH when ATA device
 fell off

On 19/12/2022 12:59, yangxingui wrote:
>> Firstly, I think that there is a bug in sas_ata_device_link_abort() -> 
>> ata_link_abort() code in that the host lock in not grabbed, as the 
>> comment in ata_port_abort() mentions. Having said that, libsas had 
>> already some dodgy host locking usage - specifically dropping the lock 
>> for the queuing path (that's something else to be fixed up ... I think 
>> that is due to queue command CB calling task_done() in some cases), 
>> but I still think that sas_ata_device_link_abort() should be fixed (to 
>> grab the host lock).
> ok, I agree with you very much for this, I had doubts about whether we 
> needed to grab lock before.

ok, I hope that you can fix this up separately.

>>
>> Secondly, this just seems like a half solution to the age-old problem 
>> - that is, EH eventually kicking in only after 30 seconds when a disk 
>> is removed with active IO. I say half solution as SAS disks still have 
>> this issue for libsas. Can we instead push to try to solve both of 
>> them now?
> 
> Jason said you must have such an opinion "a half solution". As libsas 
> does not have any interface to mark all outstanding commands as failed 
> for SAS disk currently and SAS disk support I/O resumable transmission 
> after intermittent disconnections

I don't know what you mean by "resumable transmission after intermittent 
disconnections".

> , so I want to optimize sata disk first.
> If we want to achieve a complete solution, perhaps we need to define 
> such an interface in libsas and implement it by lldd. My current idea is 
> to call sas_abort_task() for all outstanding commands in lldd. I wonder 
> if you approve of this?

Are you sure you mean sas_abort_task()? That is for the LLDD to issue an 
abort TMF. I assume that you mean sas_task_abort(). If so, I am not too 
keen on the idea of libsas calling into the LLDD to inform of such an 
event. Note that maybe a tagset iter function could be used by libsas to 
abort each active IO, but I don't like libsas messing with such a thing; 
in addition, there may be some conflict between libsas aborting the IO 
and the IO completing with error in the LLDD.

Please note that I need to refresh my memory on this whole EH topic...

Thanks,
John