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Date:   Wed, 27 Sep 2023 09:59:58 +0200
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Subject: Re: [RFC PATCH v2 00/18] scsi: scsi_error: Introduce new error handle
 mechanism
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To:     Wenchao Hao <haowenchao2@huawei.com>,
        Mike Christie <michael.christie@oracle.com>,
        Christoph Hellwig <hch@infradead.org>
Cc:     "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        louhongxiang@huawei.com, lixiaokeng@huawei.com
References: <20230901094127.2010873-1-haowenchao2@huawei.com>
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 <a92f5e0c-1976-4fc6-ba48-7ff49546318a@oracle.com>
 <06268327-cfed-f266-34a7-fda69411ef2a@huawei.com>
From:   Hannes Reinecke <hare@suse.de>
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On 9/26/23 14:57, Wenchao Hao wrote:
> On 2023/9/26 1:54, Mike Christie wrote:
>> On 9/25/23 10:07 AM, Wenchao Hao wrote:
>>> On 2023/9/25 22:55, Christoph Hellwig wrote:
>>>> Before we add another new error handling mechanism we need to fix the
>>>> old one first.  Hannes' work on not passing the scsi_cmnd to the 
>>>> various
>>>> reset handlers hasn't made a lot of progress in the last five years and
>>>> we'll need to urgently fix that first before adding even more
>>>> complexity.
>>>>
>>> I observed Hannes's patches posted about one year ago, it has not been
>>> applied yet. I don't know if he is still working on it.
>>>
>>> My patches do not depend much on that work, I think the conflict can be
>>> solved fast between two changes.
>>
>> I think we want to figure out Hannes's patches first.
>>
>> For a new EH design we will want to be able to do multiple TMFs in 
>> parallel
>> on the same host/target right?
>>
> 
> It's not necessary to do multiple TMFs in parallel, it's ok to make sure
> each TMFs do not affect each other.
> 
> For example, we have two devices: 0:0:0:0 and 0:0:0:1
> 
> Both of them request device reset, they do not happened in parallel, but
> would in serial. If 0:0:0:0 is performing device reset in progress, 0:0:0:1
> just wait 0:0:0:0 to finish.
> 
Well, not quite. Any higher-order TMFs are serialized by virtue of 
SCSI-EH, but command aborts (which also devolve down to TMFs on certain 
drivers) do run in parallel, and there we will be requiring multiple TMFs.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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