linux-kernel - Re: [PATCH v2 2/2] of: __of_detach_node()

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Message-ID: <87pntys8lm.fsf@concordia.ellerman.id.au>
Date:   Wed, 19 Dec 2018 10:44:53 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
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 v2 2/2] of: __of_detach_node() - remove node from phandle cache

Rob Herring <robh+dt@...nel.org> writes:
> On Tue, Dec 18, 2018 at 2:33 PM Frank Rowand <frowand.list@...il.com> wrote:
>>
>> On 12/18/18 12:09 PM, Frank Rowand wrote:
>> > On 12/18/18 12:01 PM, Rob Herring wrote:
>> >> On Tue, Dec 18, 2018 at 12:57 PM Frank Rowand <frowand.list@...il.com> wrote:
>> >>>
>> >>> On 12/17/18 2:52 AM, Michael Ellerman wrote:
>> >>>> Hi Frank,
>> >>>>
>> >>>> frowand.list@...il.com writes:
>> >>>>> From: Frank Rowand <frank.rowand@...y.com>
>> >>>>>
>> >>>>> Non-overlay dynamic devicetree node removal may leave the node in
>> >>>>> the phandle cache.  Subsequent calls to of_find_node_by_phandle()
>> >>>>> will incorrectly find the stale entry.  Remove the node from the
>> >>>>> cache.
>> >>>>>
>> >>>>> Add paranoia checks in of_find_node_by_phandle() as a second level
>> >>>>> of defense (do not return cached node if detached, do not add node
>> >>>>> to cache if detached).
>> >>>>>
>> >>>>> Reported-by: Michael Bringmann <mwb@...ux.vnet.ibm.com>
>> >>>>> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
>> >>>>> ---
>> >>>>
>> >>>> Similarly here can we add:
>> >>>>
>> >>>> Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
>> >>>
>> >>> Yes, thanks.
>> >>>
>> >>>
>> >>>> Cc: stable@...r.kernel.org # v4.17+
>> >>>
>> >>> Nope, 0b3ce78e90fc does not belong in stable (it is a feature, not a bug
>> >>> fix).  So the bug will not be in stable.
>> >>
>> >> 0b3ce78e90fc landed in v4.17, so Michael's line above is correct.
>> >> Annotating it with 4.17 only saves Greg from trying and then emailing
>> >> us to backport this patch as it wouldn't apply.
>> >
>> > Thanks for the correction.  I was both under-thinking and over-thinking,
>> > ending up with an incorrect answer.
>> >
>> > Can you add the Cc: to version 3 patch comments (both 1/2 and 2/2) or do
>> > you want me to re-spin?
>>
>> Now that my thinking has been straightened out, a little bit more checking
>> for the other pre-requisite patches show:
>>
>>   v4.18: commit b9952b5218ad ("of: overlay: update phandle cache on overlay apply and remove")
>>   v4.19: commit e54192b48da7 ("of: fix phandle cache creation for DTs with no phandles")
>>
>> These can be addressed by changing the "Cc:" to ... # v4.19+
>> because stable v4.17.* and v4.18.* are end of life.
>
> EOL shouldn't factor into it. There's always the possibility someone
> else picks any kernel version.

Yeah, there are other stable branches out there, so the tag should point
to the correct version regardless of whether it's currently EOL on
kernel.org.

>> Or the pre-requisites can be listed:
>>
>>    # v4.17: b9952b5218ad of: overlay: update phandle cache
>>    # v4.17: e54192b48da7 of: fix phandle cache creation
>>    # v4.17
>>
>>    # v4.18: e54192b48da7 of: fix phandle cache creation
>>    # v4.18
>>
>>    # v4.19+
>>
>> Do you have a preference?
>
> I think we just list v4.17 and be done with it.

Yep, anyone who wants to backport it can work it out, or ask us.

cheers