linux-kernel - Re: [RFC PATCH] scsi: libsas: fix WARN on device removal

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Message-ID: <CAPcyv4g+XzCuHsUvqeE+r8hqgPK3yq=E9k23a89XcLs96bkphg@mail.gmail.com>
Date:   Wed, 9 Nov 2016 11:09:17 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     John Garry <john.garry@...wei.com>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        jejb@...ux.vnet.ibm.com, linux-scsi <linux-scsi@...r.kernel.org>,
        john.garry2@...l.dcu.ie, linuxarm@...wei.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        lindar_liu@...sh.com, jinpu.wang@...fitbricks.com,
        Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] scsi: libsas: fix WARN on device removal

On Wed, Nov 9, 2016 at 9:36 AM, John Garry <john.garry@...wei.com> wrote:
> On 09/11/2016 12:28, John Garry wrote:
>>
>> On 03/11/2016 14:58, John Garry wrote:
>>>
>>> The following patch introduces an annoying WARN
>>> when a device is removed from the SAS topology:
>>> [SCSI] libsas: prevent domain rediscovery competing with ata error
>>> handling
>>>
>>
>> Are there any views on this patch? I would have thought that the parties
>> who use the drivers based on libsas would be interested in fixing this
>> bug.
>>
>
> I should have added the before and after logs earlier, so the issue is
> illustrated. Now attached. When a 24-port expander is unplugged we get >6k
> lines of WARN on the console, lasting >30 seconds. Not nice.
>

I might be mistaken, but this patch seems functionally identical to
this attempt:

http://marc.info/?l=linux-scsi&m=143459794823595&w=2

i.e. it moves the port destruction to the workqueue and still suffers
from the flutter problem:

http://marc.info/?l=linux-scsi&m=143801026028006&w=2
http://marc.info/?l=linux-scsi&m=143801971131073&w=2

Perhaps we instead need to quiet this warning?

http://marc.info/?l=linux-scsi&m=143802229932175&w=2