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References: <20210907085946.21694-1-vulab@iscas.ac.cn> <0fa7ddfa-cd65-583e-a83f-4cbcd4e7337f@linux.ibm.com>
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From:   "Oliver O'Halloran" <oohall@gmail.com>
Date:   Wed, 8 Sep 2021 09:17:49 +1000
Message-ID: <CAOSf1CGEAhXzqEU_-F39um8ri98r1Ww+AtsXJqZu4U7a_ODi9w@mail.gmail.com>
Subject: Re: [PATCH] pci/hotplug/pnv-php: Remove probable double put
To:     Tyrel Datwyler <tyreld@linux.ibm.com>
Cc:     Xu Wang <vulab@iscas.ac.cn>, Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Sep 8, 2021 at 8:02 AM Tyrel Datwyler <tyreld@linux.ibm.com> wrote:
>
> On 9/7/21 1:59 AM, Xu Wang wrote:
> > Device node iterators put the previous value of the index variable,
> > so an explicit put causes a double put.
> >
> > Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
> > ---
> >  drivers/pci/hotplug/pnv_php.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
> > index 04565162a449..ed4d1a2c3f22 100644
> > --- a/drivers/pci/hotplug/pnv_php.c
> > +++ b/drivers/pci/hotplug/pnv_php.c
> > @@ -158,7 +158,6 @@ static void pnv_php_detach_device_nodes(struct device_node *parent)
> >       for_each_child_of_node(parent, dn) {
> >               pnv_php_detach_device_nodes(dn);
> >
> > -             of_node_put(dn);
> >               of_detach_node(dn);
>
> Are you sure this is a double put? This looks to me like its meant to drive tear
> down of the device by putting a long term reference and not the short term get
> that is part of the iterator.

Yeah, the put is there is to drop the initial ref so the node can be
released. It might be worth adding a comment.