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Re: [patch 1/3] tty: resolve tty contention between kernel and user space

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On Sun, Jul 9, 2017 at 2:41 PM, Okash Khawaja <okash.khawaja@gmail.com> wrote:

> +struct tty_struct *tty_kopen(dev_t device)
> +{
> +       struct tty_struct *tty;
> +       struct tty_driver *driver = NULL;
> +       int index = -1;
> +
> +       mutex_lock(&tty_mutex);
> +       driver = tty_lookup_driver(device, NULL, &index);
> +       if (IS_ERR(driver)) {

> +               mutex_unlock(&tty_mutex);
> +               return ERR_CAST(driver);

Hmm... perhaps

tty = ERR_CAST(driver);
goto out_unlock;

See below for further details.

> +       }
> +
> +       /* check whether we're reopening an existing tty */
> +       tty = tty_driver_lookup_tty(driver, NULL, index);
> +       if (IS_ERR(tty))
> +               goto out;
> +
> +       if (tty) {
> +               /* drop kref from tty_driver_lookup_tty() */
> +               tty_kref_put(tty);
> +               tty = ERR_PTR(-EBUSY);
> +       } else { /* tty_init_dev returns tty with the tty_lock held */
> +               tty = tty_init_dev(driver, index);
> +               set_bit(TTY_KOPENED, &tty->flags);
> +       }

> +out:

out_unlock: ?

> +       mutex_unlock(&tty_mutex);
> +       tty_driver_kref_put(driver);

I'm not sure I understand locking model here:

Above
1. take mutex
2. take reference

Here:
1. give mutex back
2. give reference back

I think we usually see symmetrical  calls, i.e.

1. give reference back
2. give mutex back

So, what did I miss?

> +       return tty;
> +}



-- 
With Best Regards,
Andy Shevchenko

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Thread

tty contention resulting from tty_open_by_device export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-07 22:30 +0200
  Re: tty contention resulting from tty_open_by_device export Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-08 10:40 +0200
    Re: tty contention resulting from tty_open_by_device export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-08 11:10 +0200
    [patch 3/3] tty: undo export of tty_open_by_driver Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 13:50 +0200
    [patch 0/3] Re: tty contention resulting from tty_open_by_device export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 13:50 +0200
      [patch 2/3] staging: speakup: use tty_kopen instead of tty_open_by_driver Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 13:50 +0200
        Re: [patch 2/3] staging: speakup: use tty_kopen instead of  tty_open_by_driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-09 14:00 +0200
          Re: [patch 2/3] staging: speakup: use tty_kopen instead of  tty_open_by_driver Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 14:30 +0200
      [patch 1/3] tty: resolve tty contention between kernel and user space Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 13:50 +0200
        Re: [patch 1/3] tty: resolve tty contention between kernel and user  space Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-09 14:00 +0200
        Re: [patch 1/3] tty: resolve tty contention between kernel and user space Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-09 17:10 +0200
          Re: [patch 1/3] tty: resolve tty contention between kernel and user  space Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 21:10 +0200
          Re: [patch 1/3] tty: resolve tty contention between kernel and user  space Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-10 10:40 +0200
            Re: [patch 1/3] tty: resolve tty contention between kernel and user space Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-10 17:30 +0200
              Re: [patch 1/3] tty: resolve tty contention between kernel and user  space Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-10 18:20 +0200
      Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device  export Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-09 14:00 +0200
      [patch 4/3] tty: make tty_kopen return ENODEV in case of no TTY Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-09 14:40 +0200
      Re: [patch 0/3] Re: tty contention resulting from  tty_open_by_device export Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-07-10 14:00 +0200
        Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device  export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-10 14:40 +0200
          Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device  export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-10 18:30 +0200
          Re: [patch 0/3] Re: tty contention resulting from  tty_open_by_device export Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-07-12 20:30 +0200
            Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device  export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-13 13:40 +0200
              Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device  export Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-17 14:40 +0200
                Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-17 15:30 +0200
                Re: [patch 0/3] Re: tty contention resulting from  tty_open_by_device export Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-07-18 00:10 +0200
                [patch v2 1/3] tty: resolve tty contention between kernel and user space Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-17 23:10 +0200
                [patch v2 3/3] tty: undo export of tty_open_by_driver Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-17 23:10 +0200
                [patch v2 0/3] tty contention resulting from tty_open_by_driver export Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-17 23:10 +0200
                [patch v2 2/3] staging: speakup: use tty_kopen instead of tty_open_by_driver Okash Khawaja <okash.khawaja@gmail.com> - 2017-07-17 23:10 +0200

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