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

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Date:   Thu, 13 Dec 2018 13:57:16 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     mwb@...ux.vnet.ibm.com,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        tlfalcon@...ux.vnet.ibm.com, minkim@...ibm.com,
        devicetree@...r.kernel.org,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v03] powerpc/mobility: Fix node detach/rename problem

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.

cheers