netdev - Re: [PATCH v1] net: macb: Fix runtime PM refcounting

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Message-ID: <f301da54-3eb7-8bab-50cd-f37fc3a92b2c@microchip.com>
Date:   Thu, 30 Apr 2020 12:13:01 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <andriy.shevchenko@...ux.intel.com>
CC:     <Nicolas.Ferre@...rochip.com>, <netdev@...r.kernel.org>,
        <davem@...emloft.net>, <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH v1] net: macb: Fix runtime PM refcounting



On 30.04.2020 13:34, Andy Shevchenko wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Thu, Apr 30, 2020 at 07:59:41AM +0000, Claudiu.Beznea@...rochip.com wrote:
>>
>>
>> On 27.04.2020 13:51, Andy Shevchenko wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> The commit e6a41c23df0d, while trying to fix an issue,
>>>
>>>     ("net: macb: ensure interface is not suspended on at91rm9200")
>>>
>>> introduced a refcounting regression, because in error case refcounter
>>> must be balanced. Fix it by calling pm_runtime_put_noidle() in error case.
>>>
>>> While here, fix the same mistake in other couple of places.
> 
> ...
> 
>>>         status = pm_runtime_get_sync(&bp->pdev->dev);
>>> -       if (status < 0)
>>> +       if (status < 0) {
>>> +               pm_runtime_put_noidle(&bp->pdev->dev);
>>
>> pm_runtime_get_sync() calls __pm_runtime_resume(dev, RPM_GET_PUT),
>> increment refcounter and resume the device calling rpm_resume().
> 
> Read the code further than the header file, please.
> 
>> pm_runtime_put_noidle() just decrement the refcounter.
> 
> which is exactly what has to be done on error path.
> 
>> The proper way,
>> should be calling suspend again if the operation fails as
>> pm_runtime_put_autosuspend() does. So, what the code under mdio_pm_exit
>> label does should be enough.
> 
> Huh? It returns an error without rebalancing refcounter.

Yep, my mistake. Your code is good.


> 
> Yeah, one more time an evidence that people do not get runtime PM properly.> 
>>>                 goto mdio_pm_exit;
>>> +       }
>>>
>>>         status = macb_mdio_wait_for_idle(bp);
>>>         if (status < 0)
>>> @@ -386,8 +388,10 @@ static int macb_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>>>         int status;
>>>
>>>         status = pm_runtime_get_sync(&bp->pdev->dev);
>>> -       if (status < 0)
>>> +       if (status < 0) {
>>> +               pm_runtime_put_noidle(&bp->pdev->dev);
>>
>> Ditto.
> 
> Ditto.
> 
>>
>>>                 goto mdio_pm_exit;
>>> +       }
>>>
>>>         status = macb_mdio_wait_for_idle(bp);
>>>         if (status < 0)
>>> @@ -3816,8 +3820,10 @@ static int at91ether_open(struct net_device *dev)
>>>         int ret;
>>>
>>>         ret = pm_runtime_get_sync(&lp->pdev->dev);
>>> -       if (ret < 0)
>>> +       if (ret < 0) {
>>> +               pm_runtime_put_noidle(&lp->pdev->dev);
>>
>> The proper way should be calling pm_runtime_put_sync() not only for this
>> returning path but for all of them in this function.
> 
> Of course not.
> 
>>>                 return ret;
>>> +       }
>>>
>>>         /* Clear internal statistics */
>>>         ctl = macb_readl(lp, NCR);
>>> --
>>> 2.26.2
>>>
> 
> --
> With Best Regards,
> Andy Shevchenko
> 
>