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