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>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/char/selection.c b/drivers/char/selection.c
index 85211a3a5811..75889cd9375f 100644
--- a/drivers/char/selection.c
+++ b/drivers/char/selection.c
@@ -319,8 +319,13 @@ int paste_selection(struct tty_struct *tty)
         poke_blanked_console();
         release_console_sem();
 
-        ld = tty_ldisc_ref_wait(tty);
-        
+        ld = tty_ldisc_ref(tty);
+        if (!ld) {
+                tty_unlock();
+                ld = tty_ldisc_ref_wait(tty);
+                tty_lock();
+        }
+
         add_wait_queue(&vc->paste_wait, &wait);
         while (sel_buffer && sel_buffer_lth > pasted) {
                 set_current_state(TASK_INTERRUPTIBLE);