linux-kernel - Re: [PATCH v03] powerpc/mobility: Fix node detach/rename problem

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Date:   Fri, 14 Dec 2018 15:58:49 -0600
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, tlfalcon@...ux.vnet.ibm.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        minkim@...ibm.com, Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v03] powerpc/mobility: Fix node detach/rename problem

On 12/12/2018 08:57 PM, Michael Ellerman wrote:
> Frank Rowand <frowand.list@...il.com> writes:
>> On 12/11/18 8:07 AM, Rob Herring wrote:
>>> On Tue, Dec 11, 2018 at 7:29 AM Michael Ellerman <mpe@...erman.id.au> wrote:
> ...
>>>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>>>> index 09692c9b32a7..d8e4534c0686 100644
>>>> --- a/drivers/of/base.c
>>>> +++ b/drivers/of/base.c
>>>> @@ -1190,6 +1190,10 @@ struct device_node *of_find_node_by_phandle(phandle handle)
>>>>                 if (phandle_cache[masked_handle] &&
>>>>                     handle == phandle_cache[masked_handle]->phandle)
>>>>                         np = phandle_cache[masked_handle];
>>>> +
>>>> +               /* If we find a detached node, remove it */
>>>> +               if (of_node_check_flag(np, OF_DETACHED))
>>>> +                       np = phandle_cache[masked_handle] = NULL;
>>
>> The bug you found exposes a couple of different issues, a little bit
>> deeper than the proposed fix.  I'll work on a fuller fix tonight or
>> tomorrow.
> 
> OK thanks.
> 
>>> I'm wondering if we should explicitly remove the node from the cache
>>> when we set OF_DETACHED. Otherwise, it could be possible that the node
>>> pointer has been freed already. Or maybe we need both?
>>
>> Yes, it should be explicitly removed.  I may also add in a paranoia check in
>> of_find_node_by_phandle().
> 
> That seems best to me.

I agree that we should do both.

> 
> cheers

Michael

-- 
Michael W. Bringmann
Linux I/O, Networking and Security Development
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com