Re: [PATCH] can: etas_es58x: fix error handling

[Vincent MAILHOL <mailhol.vincent@xxxxxxxxxx>]

Hi Pavel,

Thanks for the patch!

On Mon. 15 Nov 2021 at 05:58, Pavel Skripkin <paskripkin@xxxxxxxxx> wrote:
> When register_candev() fails there are 2 possible device states:
> NETREG_UNINITIALIZED and NETREG_UNREGISTERED. None of them are suitable
> for calling unregister_candev(), because of following checks in
> unregister_netdevice_many():
>
>         if (dev->reg_state == NETREG_UNINITIALIZED)
>                 WARN_ON(1);
> ...
>         BUG_ON(dev->reg_state != NETREG_REGISTERED);
>
> To avoid possible BUG_ON or WARN_ON let's free current netdev before
> returning from es58x_init_netdev() and leave others (registered)
> net devices for es58x_free_netdevs().
>
> Fixes: 004653f0abf2 ("can: etas_es58x: add es58x_free_netdevs() to factorize code")

Fixes: 8537257874e9 ("can: etas_es58x: add core support for ETAS ES58X
CAN USB interfaces")

The bug existed from the initial commit.  Prior to the
introduction of es58x_free_netdevs(), unregister_candev() was
called in the error handling of es58x_probe():

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/can/usb/etas_es58x/es58x_core.c?id=8537257874e949a59c834cecfd5a063e11b64b0b#n2234

> Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
> ---
>  drivers/net/can/usb/etas_es58x/es58x_core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c b/drivers/net/can/usb/etas_es58x/es58x_core.c
> index 96a13c770e4a..41c721f2fbbe 100644
> --- a/drivers/net/can/usb/etas_es58x/es58x_core.c
> +++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
> @@ -2098,8 +2098,11 @@ static int es58x_init_netdev(struct es58x_device *es58x_dev, int channel_idx)
>         netdev->flags |= IFF_ECHO;      /* We support local echo */
>
>         ret = register_candev(netdev);
> -       if (ret)
> +       if (ret) {
> +               free_candev(netdev);
> +               es58x_dev->netdev[channel_idx] = NULL;

A nitpick, but if you don’t mind, I would prefer to set
es58x_dev->netdev[channel_idx] after register_candev() succeeds
so that we do not have to reset it to NULL in the error handling.

diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c
b/drivers/net/can/usb/etas_es58x/es58x_core.c
index ce2b9e1ce3af..fb0daad9b9c8 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
@@ -2091,18 +2091,20 @@ static int es58x_init_netdev(struct
es58x_device *es58x_dev, int channel_idx)
                return -ENOMEM;
        }
        SET_NETDEV_DEV(netdev, dev);
-       es58x_dev->netdev[channel_idx] = netdev;
        es58x_init_priv(es58x_dev, es58x_priv(netdev), channel_idx);

        netdev->netdev_ops = &es58x_netdev_ops;
        netdev->flags |= IFF_ECHO;      /* We support local echo */

        ret = register_candev(netdev);
-       if (ret)
+       if (ret) {
+               free_candev(netdev);
                return ret;
+       }

        netdev_queue_set_dql_min_limit(netdev_get_tx_queue(netdev, 0),
                                       es58x_dev->param->dql_min_limit);
+       es58x_dev->netdev[channel_idx] = netdev;

        return ret;
 }

>                 return ret;
> +       }
>
>         netdev_queue_set_dql_min_limit(netdev_get_tx_queue(netdev, 0),
>                                        es58x_dev->param->dql_min_limit);