linux-kernel - Re: [PATCH] pci-error-recover: doc cleanup

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Message-ID: <CAHrUA35PMscQrohN_wPgip2tM-+OiHmQT1_uhPc75=GeHvkpaw@mail.gmail.com>
Date:   Fri, 9 Dec 2016 14:24:26 +0800
From:   Linas Vepstas <linasvepstas@...il.com>
To:     Cao jin <caoj.fnst@...fujitsu.com>
Cc:     Jonathan Corbet <corbet@....net>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] pci-error-recover: doc cleanup

I suppose I'm confused, but I recall that link resets are non-fatal.
Fatal errors typically require that the the pci adapter be completely
reset, any adapter firmware to be reloaded from scratch, the device
driver has to kill all device state and start from scratch. Its huge.
If the fatal error is on pci device that is under a block device
holding a file system, then (usually) there is no way to recover,
because the block layer (and file system) cannot deal with a block
device that disappeared and then reappeared some few seconds later.
(maybe some future zfs or lvm or btrfs might be able to deal with
this, but not today)

By contrast, link resets are far more gentle: the device driver might
have to discard some half-full FIFO's, or cancel some in-flight
commands, but can otherwise gracefully recover without telling the
higher layers that there were any problems.

--linas

On Thu, Dec 8, 2016 at 10:13 PM, Cao jin <caoj.fnst@...fujitsu.com> wrote:
>
>
> On 12/08/2016 10:05 PM, Jonathan Corbet wrote:
>> On Thu, 8 Dec 2016 16:16:14 +0800
>> Cao jin <caoj.fnst@...fujitsu.com> wrote:
>>
>>>  The platform resets the link, and then calls the link_reset() callback
>>>  on all affected device drivers.  This is a PCI-Express specific state
>>> -and is done whenever a non-fatal error has been detected that can be
>>> +and is done whenever a fatal error has been detected that can be
>>>  "solved" by resetting the link. This call informs the driver of the
>>
>> As far as I can tell, the original text was correct here; why do you
>> think this change needs to be made?
>>
>
> See do_recovery() in aer core, reset_link() is called only seeing fatal
> error.
>
> --
> Sincerely,
> Cao jin
>
>