linux-kernel - Re: [PATCH v13 0/6] Address error and recovery for AER and DPC

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Date:   Mon, 16 Apr 2018 19:42:44 +0530
From:   poza@...eaurora.org
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dongdong Liu <liudongdong3@...wei.com>,
        Keith Busch <keith.busch@...el.com>, Wei Zhang <wzhang@...com>,
        Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH v13 0/6] Address error and recovery for AER and DPC

On 2018-04-16 18:57, Bjorn Helgaas wrote:
> On Mon, Apr 16, 2018 at 11:33:13AM +0530, poza@...eaurora.org wrote:
>> On 2018-04-16 09:23, Sinan Kaya wrote:
>> > On 4/15/2018 11:16 PM, Bjorn Helgaas wrote:
>> > > On Mon, Apr 09, 2018 at 10:41:48AM -0400, Oza Pawandeep wrote:
>> > > > This patch set brings in error handling support for DPC
>> > > >
>> > > > The current implementation of AER and error message broadcasting
>> > > > to the
>> > > > EP driver is tightly coupled and limited to AER service driver.
>> > > > It is important to factor out broadcasting and other link handling
>> > > > callbacks. So that not only when AER gets triggered, but also
>> > > > when DPC get
>> > > > triggered (for e.g. ERR_FATAL), callbacks are handled appropriately.
>> > > >
>> > > > DPC should behave identical to AER as far as error handling is
>> > > > concerned.
>> > > > DPC should remove the devices and not to do recovery for hotplug
>> > > > enabled system.
>> > >
>> > > Is there a specific bug that's fixed by these patches?  I didn't see
>> > > one mentioned in the changelogs.
>> > >
>> >
>> > There is no actual bug.
>> >
>> > We realized that DPC and hotplug is heavily integrated today. We
>> > have use cases for systems without hotplug support but still
>> > support DPC. That's the problem we are trying to solve with this
>> > patchset.
> 
> Apparently there's a problem with systems that have DPC but not
> hotplug.  It will be extremely helpful if you can articulate what that
> problem is and include it in the appropriate changelog.
> 
>> Adding to what Sinan said;
>> 
>> DPC should handle the error handling and recovery similar to AER,
>> because finally both are attempting recovery in some or the other
>> way, and for that error handling and recovery framework has to be
>> loosely coupled.  It achieves uniformity and transparency to the
>> error handling agents such as AER, DPC, with respect to recovery and
>> error handling.
>> 
>> So, this patch-set tries to unify lot of things between error agents
>> and make them behave in a well defined way. (be it error (FATAL,
>> NON_FATAL) handling or recovery).
> 
> I totally support this objective.

Thanks Bjorn, I will include this objective in Changelog along with 
Sinan's text.
I am not clear on one last thing Bjorn; which is;
do we need last patch ? patch-6 which handles hotplug case.
Also I think we could take this patch-set as basic changes/attempt to 
unify the code which it does.

And, in the next follow-up patches we can improve upon the things such 
as,
whether to do different actions for FATAL cases and NON_FATAL cases. And 
then I can make needed changes to AER and DPC
Please let me know how this sounds.

> 
> Bjorn