linux-kernel - Re: [PATCH] arm/mach-at91/pm: Do not double put the device node

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Date:   Thu, 16 Aug 2018 12:32:57 +0300
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        zhong jiang <zhongjiang@...wei.com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux@...linux.org.uk>
Subject: Re: [PATCH] arm/mach-at91/pm: Do not double put the device node

Hi Alexandre,

On 14.08.2018 15:59, Alexandre Belloni wrote:
> On 14/08/2018 09:54:56+0800, zhong jiang wrote:
>> Device node iterators put the previous value of the index variable,
>> so an explicit put causes a double put.
>>
> 
> While for_each_matching_node_and_match will get and put the node
> properly, there is also a call to of_find_device_by_node that will get a
> reference to the node.
> 

Looking through of_find_device_by_node() it seems that a put_device() on the
struct device member of the returned struct platform_device has to be called
instead of of_node_put().

of_find_device_by_node() calls bus_find_device():

dev = bus_find_device(&platform_bus_type, NULL, np, of_dev_node_match); 

the match function, of_dev_node_match(), is just as follows:

static int of_dev_node_match(struct device *dev, void *data)                    
{                                                                               
        return dev->of_node == data;                                            
}                                                                               

but bus_find_device() takes a reference to the struct device returned in case it
founds a match, via get_device():

struct device *bus_find_device(struct bus_type *bus,                            
                               struct device *start, void *data,                
                               int (*match)(struct device *dev,
			       void*data))    
{                                                                               
        struct klist_iter i;                                                    
        struct device *dev;                                                     
                                                                                
        if (!bus || !bus->p)                                                    
                return NULL;                                                    
                                                                                
        klist_iter_init_node(&bus->p->klist_devices, &i,                        
                             (start ? &start->p->knode_bus : NULL));            
        while ((dev = next_device(&i)))                                         
                if (match(dev, data) && get_device(dev))                        
                        break;                                                  
        klist_iter_exit(&i);                                                    
        return dev;                                                             
}                                                                               

So, I think a put_device(&pdev->dev) has to be called in at91_pm_config_ws()
instead of of_node_put(np). My bad!

Thank you,
Claudiu Beznea

>> I detect the issue with the help of Coccinelle.
>>
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
>> ---
>>  arch/arm/mach-at91/pm.c | 5 +----
>>  1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c
>> index 32fae4d..a5ec35f 100644
>> --- a/arch/arm/mach-at91/pm.c
>> +++ b/arch/arm/mach-at91/pm.c
>> @@ -143,15 +143,12 @@ static int at91_pm_config_ws(unsigned int pm_mode, bool set)
>>  
>>  			/* Check if enabled on SHDWC. */
>>  			if (wsi->shdwc_mr_bit && !(val & wsi->shdwc_mr_bit))
>> -				goto put_node;
>> +				continue;
>>  
>>  			mode |= wsi->pmc_fsmr_bit;
>>  			if (wsi->set_polarity)
>>  				polarity |= wsi->pmc_fsmr_bit;
>>  		}
>> -
>> -put_node:
>> -		of_node_put(np);
>>  	}
>>  
>>  	if (mode) {
>> -- 
>> 1.7.12.4
>>
>