From: Peter Hurley <peter@hurleysoftware.com>
Date: Sat, 15 Jun 2013 11:28:30 +0000 (-0400)
Subject: n_tty: Fix unsafe update of available buffer space
X-Git-Tag: omap-for-v3.11/fixes-for-merge-window~77^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b84830527645dfe7b7a5cc03518e3c791b4ee9e0;p=pandora-kernel.git

n_tty: Fix unsafe update of available buffer space

receive_room is used to control the amount of data the flip
buffer work can push to the read buffer. This update is unsafe:

  CPU 0                        |  CPU 1
                               |
                               | n_tty_read()
                               |   n_tty_set_room()
                               |     left = <calc of space>
n_tty_receive_buf()            |
  <push data to buffer>        |
  n_tty_set_room()             |
    left = <calc of space>     |
    tty->receive_room = left   |
                               |     tty->receive_room = left

receive_room is now updated with a stale calculation of the
available buffer space, and the subsequent work loop will likely
overwrite unread data in the input buffer.

Update receive_room atomically with the calculation of the
available buffer space.

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

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