linux-kernel - Re: [PATCH v2] iio:core: In map_array_register() cleanup in case of error

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Message-ID: <CAHp75VfQ=fFn_r43VPV0uPCkozS2K=VQsuSEyj0mF+7QVsFQuA@mail.gmail.com>
Date:   Fri, 16 Oct 2020 18:09:48 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald <pmeerw@...erw.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iio:core: In map_array_register() cleanup in case of error

On Sun, Oct 11, 2020 at 9:24 PM Lino Sanfilippo <LinoSanfilippo@....de> wrote:
>
> In function map_array_register() properly rewind in case of error.
> Furthermore remove the now superfluous initialization of "ret" with 0.

>  int iio_map_array_register(struct iio_dev *indio_dev, struct iio_map *maps)
>  {
> -       int i = 0, ret = 0;
> +       int i = 0, ret;
>         struct iio_map_internal *mapi;
>
>         if (maps == NULL)
> @@ -44,7 +44,18 @@ int iio_map_array_register(struct iio_dev *indio_dev, struct iio_map *maps)
>                 list_add_tail(&mapi->l, &iio_map_list);
>                 i++;
>         }
> +       mutex_unlock(&iio_map_list_lock);
> +
> +       return 0;
> +
>  error_ret:

Wait a bit.
First of all we linked all successfully added items to the list.
>From this we have two ways to go:
 - leave with as many maps as we registered
 - clean up and bail out

I dunno which one would play better in IIO, but you seem to go with
the latter one.

> +       /* undo */
> +       while (i--) {
> +               mapi = list_last_entry(&iio_map_list, struct iio_map_internal,
> +                                      l);
> +               list_del(&mapi->l);
> +               kfree(mapi);
> +       }

We have iio_map_array_unregister(). Why not use it?

>         mutex_unlock(&iio_map_list_lock);

I would rather drop a label with replacement goto -> break inside the
loop and call the following


        mutex_unlock(&iio_map_list_lock);
if (ret)
  iio_map_array_unregister();
return ret;

Sounds like only a few LOCs are needed.

-- 
With Best Regards,
Andy Shevchenko