Re: [PATCH -next 00/27] tty locking changes

One Thousand Gnomes
2014-10-22T15:32:03Z

On Thu, 16 Oct 2014 16:24:58 -0400
Peter Hurley <peter@hurleysoftware.com> wrote:

> Hi Greg,
>
> This patch series has 3 major changes to how tty locking behaves:
> 1. the lock order of tty_lock() and tty->ldisc_sem is reversed;
> this eliminates a bunch of lock drop/reacquire which, in turn,
> eliminates tty state tracking that can no longer be observed.
> This also allows the pty driver to wait for input processing to
> complete while closing before setting TTY_OTHER_CLOSED (which
> eliminates the ugliness of checking input twice in n_tty_read() and
> n_tty_poll()).
> 2. the footprint of tty_mutex is reduced to only adding and removing
> ttys and is no longer held to acquire the tty_lock() in tty_open();
> this allows for multiple ttys to be opened concurrently, even if
> one open stalls waiting for its tty_lock().
> 3. pty pair locking is reordered to master first, then slave, rather
> than by address. This works because, while releasing the master pty,
> the slave tty count needs to be changed, whereas, when releasing the
> slave, the master pty does not need to be accessed.
> This furthur eliminates more lock drop/reacquire.
>
> The longer-term goals, which this series builds towards, is:
> 1. simplifying the tty open/close behavior
> 2. eliminating the ASYNC_CLOSING code without breaking existing userspace
> 3. eliminating returning -EIO from tty_open(). Not sure if this is possible yet.

Reviewed-by: Alan Cox <alan@linux.intel.com>