Because pty_set_pktmode() does not claim the slave's ctrl_lock
to clear ->ctrl_status (to avoid unnecessary lock nesting),
pty_set_pktmode() may accidentally erase new ->ctrl_status updates.
For example,
CPU 0 | CPU 1
pty_set_pktmode() | pty_start()
spin_lock(master's ctrl_lock) |
tty->packet = 1 |
| if (tty->link->packet)
| spin_lock(slave's ctrl_lock)
| tty->ctrl_status = TIOCPKT_START
tty->link->ctrl_status = 0 |
Ensure the clear of ->ctrl_status occurs before packet mode is set
(and observable on another cpu).
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/pty.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index e554393..bcec4c7 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -186,8 +186,9 @@ static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
spin_lock_irq(&tty->ctrl_lock);
if (pktmode) {
if (!tty->packet) {
- tty->packet = 1;
tty->link->ctrl_status = 0;
+ smp_mb();
+ tty->packet = 1;
}
} else
tty->packet = 0;
--
2.1.1
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