From: Peter Hurley <peter@hurleysoftware.com>
Date: Sat, 15 Jun 2013 13:14:26 +0000 (-0400)
Subject: n_tty: Make N_TTY ldisc receive path lockless
X-Git-Tag: v3.12-rc1~182^2~208
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6d76bd2618535c581f1673047b8341fd291abc67;p=pandora-kernel.git

n_tty: Make N_TTY ldisc receive path lockless

n_tty has a single-producer/single-consumer input model;
use lockless publish instead.

Use termios_rwsem to exclude both consumer and producer while
changing or resetting buffer indices, eg., when flushing. Also,
claim exclusive termios_rwsem to safely retrieve the buffer
indices from a thread other than consumer or producer
(eg., TIOCINQ ioctl).

Note the read_tail is published _after_ clearing the newline
indicator in read_flags to avoid racing the producer.

Drop read_lock spinlock.

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