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tty: Convert tty_struct bitfield to ints 

The stopped, hw_stopped, flow_stopped and packet bits are smp-unsafe
and interrupt-unsafe. For example,

CPU 0                         | CPU 1
                              |
tty->flow_stopped = 1         | tty->hw_stopped = 0

One of these updates will be corrupted, as the bitwise operation
on the bitfield is non-atomic.

Ensure each flag has a separate memory location, so concurrent
updates do not corrupt orthogonal states. Because DEC Alpha EV4 and EV5
cpus (from 1995) perform RMW on smaller-than-machine-word storage,
"separate memory location" must be int instead of byte.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2014-09-10 15:06:30 -04:00 committed by Greg Kroah-Hartman
parent 938f7e13b5
commit d7a855bd6a
1 changed files with 4 additions and 1 deletions
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5
include/linux/tty.h
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@ -261,7 +261,10 @@ struct tty_struct {
unsigned long flags;
int count;
struct winsize winsize; /* winsize_mutex */
unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1;
int stopped;
int flow_stopped;
int hw_stopped;
int packet;
unsigned char ctrl_status; /* ctrl_lock */
unsigned int receive_room; /* Bytes free for queue */
int flow_change;