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authorPeter Hurley <peter@hurleysoftware.com>2014-10-16 15:33:27 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-05 16:34:36 -0800
commit2622d73e51acfe1dbeb21bf2299066bdead85163 (patch)
tree06f2fff030593a0d730b61cd78da5923baec8683 /drivers/tty/pty.c
parent54e8e5fcaae109f0303f52efb24f29bfac79ca86 (diff)
pty: Fix packet mode setting race
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@hurleysoftware.com> Reviewed-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/pty.c')
-rw-r--r--drivers/tty/pty.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index e554393d5551..bcec4c71a408 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;

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