From: Peter Hurley <peter@hurleysoftware.com>
Date: Fri, 16 Jan 2015 20:05:37 +0000 (-0500)
Subject: n_tty: Fix unordered accesses to lockless read buffer
X-Git-Tag: fixes-v4.0-rc1~98^2~30
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=70aca71f92ca2c111978bf676287fab5580d2598;p=pandora-kernel.git

n_tty: Fix unordered accesses to lockless read buffer

Add commit_head buffer index, which the producer-side publishes
after input processing in non-canon mode. This ensures the consumer-side
observes correctly-ordered writes in non-canonical mode (ie., the buffer
data is written before the buffer index is advanced). Fix consumer-side
uses of read_cnt() to use commit_head instead.

Add required memory barriers to the tail index to guarantee
the consumer-side has completed the loads before the producer-side
begins writing new data. Open-code the producer-side receive_room()
into the i/o loop.

Remove no-longer-referenced receive_room().

Based on work by Christian Riesch <christian.riesch@omicron.at>

Cc: Christian Riesch <christian.riesch@omicron.at>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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