This fixes the lock order of the BTM and
ldisc_mutex so that we never take the BTM
while holding ldisc_mutex, which means
we no longer have to use mutex_lock_tty
when getting ldisc_mutex.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/char/tty_io.c    |    2 +-
 drivers/char/tty_ldisc.c |   15 ++++++++-------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 4e16b34..80178cc 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1289,7 +1289,7 @@ static int tty_reopen(struct tty_struct *tty)
 	tty->count++;
 	tty->driver = driver; /* N.B. why do this every time?? */
 
-	mutex_lock_tty_on(&tty->ldisc_mutex);
+	mutex_lock(&tty->ldisc_mutex);
 	WARN_ON(!test_bit(TTY_LDISC, &tty->flags));
 	mutex_unlock(&tty->ldisc_mutex);
 
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index 0c0e935..dda31b0 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -598,7 +598,8 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	tty_wait_until_sent(tty, 0);
 
-	mutex_lock_tty_off(&tty->ldisc_mutex);
+	tty_lock();
+	mutex_lock(&tty->ldisc_mutex);
 
 	/*
 	 *	We could be midstream of another ldisc change which has
@@ -607,13 +608,13 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
 		mutex_unlock(&tty->ldisc_mutex);
+		tty_unlock();
 		wait_event(tty_ldisc_wait,
 			test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
-		mutex_lock_tty_off(&tty->ldisc_mutex);
+		tty_lock();
+		mutex_lock(&tty->ldisc_mutex);
 	}
 
-	tty_lock();
-
 	set_bit(TTY_LDISC_CHANGING, &tty->flags);
 
 	/*
@@ -650,8 +651,8 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	flush_scheduled_work();
 
-	mutex_lock_tty_off(&tty->ldisc_mutex);
 	tty_lock();
+	mutex_lock(&tty->ldisc_mutex);
 	if (test_bit(TTY_HUPPED, &tty->flags)) {
 		/* We were raced by the hangup method. It will have stomped
 		   the ...
[ message continues ]

Ignore this one, I just realized that we're releasing
and reacquiring the BTM in tty_ldisc_halt,
tty_set_termios_ldisc and possibly others.

This patch needs more work to make that possible.

	Arnd
--

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