From: Peter Hurley <peter@hurleysoftware.com>
Date: Wed, 10 Sep 2014 19:06:31 +0000 (-0400)
Subject: tty: Serialize tty flow control changes with flow_lock
X-Git-Tag: fixes-for-v3.18-merge-window~14^2~29
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f9e053dcfc02b0ad29daec8524fb1afe09774976;p=pandora-kernel.git

tty: Serialize tty flow control changes with flow_lock

Without serialization, the flow control state can become inverted
wrt. the actual hardware state. For example,

CPU 0                          | CPU 1
stop_tty()                     |
  lock ctrl_lock               |
  tty->stopped = 1             |
  unlock ctrl_lock             |
                               | start_tty()
                               |   lock ctrl_lock
                               |   tty->stopped = 0
                               |   unlock ctrl_lock
                               |   driver->start()
  driver->stop()               |

In this case, the flow control state now indicates the tty has
been started, but the actual hardware state has actually been stopped.

Introduce tty->flow_lock spinlock to serialize tty flow control changes.
Split out unlocked __start_tty()/__stop_tty() flavors for use by
ioctl(TCXONC) in follow-on patch.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

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