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

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Date:   Thu, 30 Apr 2020 07:59:41 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <andriy.shevchenko@...ux.intel.com>, <Nicolas.Ferre@...rochip.com>,
        <netdev@...r.kernel.org>, <davem@...emloft.net>
CC:     <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH v1] net: macb: Fix runtime PM refcounting



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.
> 
> Fixes: e6a41c23df0d ("net: macb: ensure interface is not suspended on at91rm9200")
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Claudiu Beznea <claudiu.beznea@...rochip.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index a0e8c5bbabc01..f739d16d29b1d 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -334,8 +334,10 @@ static int macb_mdio_read(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);

pm_runtime_get_sync() calls __pm_runtime_resume(dev, RPM_GET_PUT),
increment refcounter and resume the device calling rpm_resume().

pm_runtime_put_noidle() just decrement the refcounter. 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.

>                 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.

>                 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.

>                 return ret;
> +       }
> 
>         /* Clear internal statistics */
>         ctl = macb_readl(lp, NCR);
> --
> 2.26.2
>