Date: Wed, 22 Oct 2014 16:31:46 +0100
From: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, Jiri Slaby <jslaby@suse.cz>,
        linux-serial@vger.kernel.org
Subject: Re: [PATCH -next 00/27] tty locking changes
Message-ID: <20141022163146.73967b1e@alan.etchedpixels.co.uk>
In-Reply-To: <1413491125-20134-1-git-send-email-peter@hurleysoftware.com>
References: <1413491125-20134-1-git-send-email-peter@hurleysoftware.com>
Organization: Intel Corporation
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org

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>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/