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Commit d7a855bd authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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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: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 938f7e13

include/linux/tty.h

+4 −1
Original line number Diff line number Diff line
@@ -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;