linux-kernel - Re:Re: [PATCH v2] arch: powerpc: platforms: 85xx: Add missing of_node_put in sgy

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Message-ID: <87ilozc3qp.fsf@mpe.ellerman.id.au>
Date:   Fri, 17 Jun 2022 14:29:02 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Liang He <windhl@....com>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        oss@...error.net, paulus@...ba.org, christophe.leroy@...roup.eu,
        nixiaoming@...wei.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH v2] arch: powerpc: platforms: 85xx: Add missing
 of_node_put in sgy_cts1000.c

"Liang He" <windhl@....com> writes:
> At 2022-06-17 07:37:06, "Michael Ellerman" <mpe@...erman.id.au> wrote:
>>Christophe JAILLET <christophe.jaillet@...adoo.fr> writes:
>>> Le 16/06/2022 à 17:19, Liang He a écrit :
>>>> In gpio_halt_probe(), of_find_matching_node() will return a node pointer with
>>>> refcount incremented. We should use of_node_put() in each fail path or when it
>>>> is not used anymore.
>>>> 
>>>> Signed-off-by: Liang He <windhl@....com>
>>>> ---
>>>>   changelog:
>>>> 
>>>>   v2: use goto-label patch style advised by Christophe.
>>>>   v1: add of_node_put() before each exit.
>>>> 
>>>>   arch/powerpc/platforms/85xx/sgy_cts1000.c | 27 +++++++++++++++--------
>>>>   1 file changed, 18 insertions(+), 9 deletions(-)
>>>> 
>>>> diff --git a/arch/powerpc/platforms/85xx/sgy_cts1000.c b/arch/powerpc/platforms/85xx/sgy_cts1000.c
>>>> index 98ae64075193..e280f963d88c 100644
>>>> --- a/arch/powerpc/platforms/85xx/sgy_cts1000.c
>>>> +++ b/arch/powerpc/platforms/85xx/sgy_cts1000.c
>>>> @@ -73,6 +73,7 @@ static int gpio_halt_probe(struct platform_device *pdev)
>>...
>>>> @@ -122,8 +127,12 @@ static int gpio_halt_probe(struct platform_device *pdev)
>>>>   
>>>>   	printk(KERN_INFO "gpio-halt: registered GPIO %d (%d trigger, %d"
>>>>   	       " irq).\n", gpio, trigger, irq);
>>>> +	ret = 0;
>>>>   
>>>> -	return 0;
>>>> +err_put:
>>>> +	of_node_put(halt_node);
>>>> +	halt_node = NULL;
>>>
>>> Hi,
>>> so now we set 'halt_node' to NULL even in the normal case.
>>> This is really spurious.
>>>
>>> Look at gpio_halt_cb(), but I think that this is just wrong and badly 
>>> breaks this driver.
>>
>>I agree, thanks for reviewing.
>>
>>I think the cleanest solution is to use a local variable for the node in
>>the body of gpio_halt_probe(), and only assign to halt_node once all the
>>checks have passed.
>>
>>So something like:
>>
>>        struct device_node *child_node;
>>
>>	child_node = of_find_matching_node(node, child_match);
>>        ...
>>
>>	printk(KERN_INFO "gpio-halt: registered GPIO %d (%d trigger, %d"
>>	       " irq).\n", gpio, trigger, irq);
>>        ret = 0;
>>        halt_node = of_node_get(child_node);
>>
>>out_put:
>>        of_node_put(child_node);
>>        
>>	return ret;
>>}
>>
>>
>>cheers
>
> Hi, Michael and Christophe,
>
> I am writing the new patch based on Michael's advice. However, I wonder if there is
> any place to call of_node_put(halt_node)?  As I do not exactly know if gpio_halt_remove()
> or anyother place can correctly release this global reference？
> If not, it is correct that I add a of_node_put(halt_node) in gpio_halt_remove(), right?

Yes I think so, just before it's set to NULL, eg:

diff --git a/arch/powerpc/platforms/85xx/sgy_cts1000.c b/arch/powerpc/platforms/85xx/sgy_cts1000.c
index 98ae64075193..7beb3cd420ba 100644
--- a/arch/powerpc/platforms/85xx/sgy_cts1000.c
+++ b/arch/powerpc/platforms/85xx/sgy_cts1000.c
@@ -139,6 +139,7 @@ static int gpio_halt_remove(struct platform_device *pdev)
 
 		gpio_free(gpio);
 
+		of_node_put(halt_node);
 		halt_node = NULL;
 	}
 

cheers