Re: [1/3] powerpc/pmac: Fix DT refcount imbalance in pmac_pic_probe_oldstyle

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Michael,

On Fri, Jan 30, 2015 at 5:09 AM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> On Wed, 2015-14-01 at 13:51:57 UTC, Geert Uytterhoeven wrote:
>> of_find_node_by_name() calls of_node_put() on its "from" parameter,
>> which must not be done on "master", as it's still in use, and will be
>> released manually later.  This may cause a zero kref refcount.
>> Use of_get_child_by_name() instead to fix this.
>
> But of_find_node_by_name() searches *all* nodes, not just the children of the
> parameter.

That's correct. However, I guess the second mac-io will just be a direct child.

> So this is a logic change AFAICS, and I have no idea what machines we'd need to
> test on to check it.

Originally it comes from arch/ppc/platforms/pmac_pic.c, added in 2002 in
full-history-linux commit 5ea3254844ae344a
("Import arch/ppc and include/asm-ppc changes from linuxppc_2_5 tree").

I've also checked my linuxppc mail archives from 1997-2002, but couldn't find
the actual patch and a description.

So I don't know on which machines it's needed.

> So I think an of_node_get(master) would be safer and also fix the refcounting.

If no one can confirm the above, that may indeed be the best solution.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds