tty: reorder ldisc locking
We need to release the BTM in paste_selection() when
sleeping in tty_ldisc_ref_wait to avoid deadlocks
with tty_ldisc_enable.
In tty_set_ldisc, we now always grab the BTM before
taking the ldisc_mutex in order to avoid AB-BA
deadlocks between the two.
tty_ldisc_halt potentially blocks on a workqueue
function that takes the BTM, so we must release
the BTM before calling it.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index 97681ff..0f49479 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -582,6 +582,7 @@
tty_wait_until_sent(tty, 0);
+ tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
@@ -591,13 +592,13 @@
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);
+ tty_lock();
mutex_lock(&tty->ldisc_mutex);
}
- tty_lock();
-
set_bit(TTY_LDISC_CHANGING, &tty->flags);
/*
@@ -634,8 +635,8 @@
flush_scheduled_work();
- mutex_lock(&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 ldisc data and closed the ldisc down */
@@ -782,7 +783,20 @@
* Avoid racing set_ldisc or tty_ldisc_release
*/
mutex_lock(&tty->ldisc_mutex);
- tty_ldisc_halt(tty);
+
+ /*
+ * this is like tty_ldisc_halt, but we need to give up
+ * the BTM before calling cancel_delayed_work_sync,
+ * which may need to wait for another function taking the BTM
+ */
+ clear_bit(TTY_LDISC, &tty->flags);
+ tty_unlock();
+ cancel_delayed_work_sync(&tty->buf.work);
+ mutex_unlock(&tty->ldisc_mutex);
+
+ tty_lock();
+ mutex_lock(&tty->ldisc_mutex);
+
/* At this point we have a closed ldisc and we want to
reopen it. We could defer this to the next open but
it means auditing a lot of other paths so this is
@@ -853,8 +867,10 @@
* race with the set_ldisc code path.
*/
+ tty_unlock();
tty_ldisc_halt(tty);
flush_scheduled_work();
+ tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*