[PATCH] tty:tty_ldisc: add tty_ldisc_lock|unlock to prevent concurrent update to ldisc in tty_ldisc_reinit

[Wang YanQing]

This patch could fix the issue that tty_reopen in tty_io
calling tty_ldisc_reinit without holding tty->ldisc_sem.

Signed-off-by: Wang YanQing <udkni...@gmail.com>
---
 drivers/tty/tty_ldisc.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index b0500a0..b1f7fa5 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -616,6 +616,10 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
        if (IS_ERR(ld))
                return PTR_ERR(ld);
 
+       /*
+        * Avoid racing set_ldisc or tty_ldisc_release
+        */
+       tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
        if (tty->ldisc) {
                tty_ldisc_close(tty, tty->ldisc);
                tty_ldisc_put(tty->ldisc);
@@ -629,6 +633,7 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
                tty_ldisc_put(tty->ldisc);
                tty->ldisc = NULL;
        }
+       tty_ldisc_unlock(tty);
        return retval;
 }
 
@@ -672,22 +677,18 @@ void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
        /*
         * Shutdown the current line discipline, and reset it to
         * N_TTY if need be.
-        *
-        * Avoid racing set_ldisc or tty_ldisc_release
         */
-       tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
-
        if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
                tty_reset_termios(tty);
 
-       if (tty->ldisc) {
-               if (reinit) {
-                       if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
-                               tty_ldisc_reinit(tty, N_TTY);
-               } else
-                       tty_ldisc_kill(tty);
+       if (reinit) {
+               if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
+                       tty_ldisc_reinit(tty, N_TTY);
+       } else {
+               tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
+               tty_ldisc_kill(tty);
+               tty_ldisc_unlock(tty);
        }
-       tty_ldisc_unlock(tty);
 }
 
 /**
-- 
1.8.5.6.2.g3d8a54e.dirty