Commit d7a855bd authored Sep 10, 2014 by Peter Hurley Committed by Greg Kroah-Hartman Sep 23, 2014

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>

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;

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