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From:   Nathan Lynch <nathanl@linux.ibm.com>
To:     Wan Jiabing <wanjiabing@vivo.com>
Cc:     kael_w@yeah.net, Wan Jiabing <wanjiabing@vivo.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        linuxppc-dev@lists.ozlabs.org, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Tyrel Datwyler <tyreld@linux.ibm.com>, ajd@linux.ibm.com
Subject: Re: [PATCH] PCI/hotplug: Remove unneeded of_node_put() in pnv_php
In-Reply-To: <20211020094604.2106-1-wanjiabing@vivo.com>
References: <20211020094604.2106-1-wanjiabing@vivo.com>
Date:   Wed, 20 Oct 2021 06:39:41 -0500
Message-ID: <87tuhcx6v6.fsf@linux.ibm.com>
MIME-Version: 1.0
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Wan Jiabing <wanjiabing@vivo.com> writes:
> Fix following coccicheck warning:
> ./drivers/pci/hotplug/pnv_php.c:161:2-13: ERROR: probable double put.
>
> Device node iterators put the previous value of the index variable, so
> an explicit put causes a double put.

I suppose Coccinelle doesn't take into account that this code is
detaching and freeing the nodes.


> diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
> index f4c2e6e01be0..f3da4f95d73f 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);
>  	}

The code might be improved by comments explaining how the bare
of_node_put() corresponds to a "get" somewhere else in the driver, and
how it doesn't render the ongoing traversal unsafe. It looks suspicious
on first review, but I believe it's intentional and probably correct as
written.