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Subject: Re: [PATCH 1/1] PCI/AER: prevent pcie_do_fatal_recovery from using
 device after it is removed
To: Keith Busch <keith.busch@intel.com>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: poza@codeaurora.org, Bjorn Helgaas <helgaas@kernel.org>,
 Thomas Tai <thomas.tai@oracle.com>, bhelgaas@google.com,
 linux-pci@vger.kernel.org, linux-pci-owner@vger.kernel.org,
 Sam Bobroff <sam.bobroff@au1.ibm.com>
References: <b2e2ac5c92d8a91d00606754d1046578@codeaurora.org>
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 <ad23b16cf7ff1f3b51961fda59533892@codeaurora.org>
 <2742bdba5ae8ccc420234b6e6b0224919367ed4c.camel@kernel.crashing.org>
 <20180821143751.GA18477@localhost.localdomain>
 <277b7056aa7af8e98d5cd912838e582783943aa9.camel@kernel.crashing.org>
 <20180821220456.GC18612@localhost.localdomain>
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 <20180830000100.GA5841@localhost.localdomain>
From: Sinan Kaya <okaya@kernel.org>
Message-ID: <3e39e860-95a6-ae17-cc89-ac9550ffca40@kernel.org>
Date: Wed, 29 Aug 2018 20:10:53 -0400
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On 8/29/2018 8:01 PM, Keith Busch wrote:
> On Wed, Aug 22, 2018 at 09:06:57AM +1000, Benjamin Herrenschmidt wrote:
>> It can be probably done by a simple test & skip as you go down
>> restoring state, then handling the removals after the dance is
>> complete.
> 
> I tested on a variety of hardware, and there are mixed results. The spec
> captures the crux of the problem with checking PDC (7.5.3.11):
> 
>    Note that the in-band presence detect mechanism requires that power be
>    applied to an adapter for its presence to be detected. Consequently,
>    form factors that require a power controller for hot-plug must implement
>    a physical pin presence detect mechanism.
> 
> Many slots don't implement power controllers, so a secondary bus reset
> always triggers a PDC. We can't really ignore PDC during fatal error
> handling since hot plugs are the types of actions that often trigger
> fatal errors..
> 
> Does it sound okay to trust PDC anyway? It's no worse than what would
> happen currently, and it doesn't affect non-hotplug slots.
> 

Why does hotplug operations cause a fatal error? DPC driver is only monitoring
fatal errors today.