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@xxxxxxxxxxxxxxxxxx>
---
include/linux/tty.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1c3316a..a707196 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -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;
--
2.1.0
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