tty: Only guarantee termios read safety for throttle/unthrottle

No tty driver modifies termios during throttle() or unthrottle().
Therefore, only read safety is required.

However, tty_throttle_safe and tty_unthrottle_safe must still be
mutually exclusive; introduce throttle_mutex for that purpose.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index d3042076d163..57a70d1d0412 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -244,6 +244,7 @@ struct tty_struct {
 
         struct mutex atomic_write_lock;
         struct mutex legacy_mutex;
+        struct mutex throttle_mutex;
         struct rw_semaphore termios_rwsem;
         spinlock_t ctrl_lock;
         /* Termios values are protected by the termios rwsem */