linux-kernel - Re: v4.17 regression: PowerMac G3 won't boot, was Re: [PATCH v5 1/3] of: cache phandle nodes to reduce cost of of_find_node_by

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Message-ID: <0ad5dbfd-08f3-b97d-34b9-70fc9a729921@gmail.com>
Date:   Thu, 30 Aug 2018 21:36:00 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Stan Johnson <userm57@...oo.com>, Rob Herring <robh+dt@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: v4.17 regression: PowerMac G3 won't boot, was Re: [PATCH v5 1/3]
 of: cache phandle nodes to reduce cost of of_find_node_by_phandle()

Hi Finn,

On 08/29/18 17:44, Finn Thain wrote:
> Hi Frank,
> 
> Linux v4.17 and later will no longer boot on a G3 PowerMac. The boot hangs 
> very early, before any video driver loads.
> 
> Stan and I were able to bisect the regression between v4.16 and v4.17 and 
> arrived at commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of 
> of_find_node_by_phandle()").
> 
> I don't see any obvious bug in 0b3ce78e90fc or b9952b5218ad. But if you 
> revert these from v4.18 (which is also affected) that certainly resolves 
> the issue.
> 
> I did see this in the kernel messages:
> 
> Duplicate name in PowerPC,750, renamed to "l2-cache#1"
> Duplicate name in mac-io, renamed to "ide#1"
> Duplicate name in ide#1, renamed to "atapi-disk#1"
> Duplicate name in multifunc-device, renamed to "pci1799,1#1"
> 
> No idea whether that's relevant; I haven't done any further investigation. 
> Complete dmesg output is attached. Please let me know if there's any more 
> information you need to help find the bug.
> 
> Thanks.

I don't have any useful answers yet, but I am following the thread and have
also quickly scanned the two commits for any obvious cause.  I will look
into this some more, but have a few other tasks that I need to complete
first.

A long shot, but something to consider, is that I failed to cover the
cases of dynamic devicetree updates (removing nodes that contain a
phandle) in ways other than overlays.  Michael Ellerman has reported
such a problem for powerpc/mobility with of_detach_node().  A patch to
fix that is one of the tasks I need to complete.

-Frank