tty: untangle locking of wait_until_sent

Some wait_until_sent versions require the big
tty mutex, others don't and some callers of
wait_until_sent already hold it while other don't.
That leads to recursive use of the BTM in these
functions, which we're trying to get rid of.

This turns all cleans up the locking there so
that the driver's wait_until_sent function
never takes the BTM itself if it is already
called with that lock held.

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, 9 insertions, 2 deletions

diff --git a/drivers/char/amiserial.c b/drivers/char/amiserial.c
index 1b21a7adeb5..8228e61bb54 100644
--- a/drivers/char/amiserial.c
+++ b/drivers/char/amiserial.c
@@ -1528,6 +1528,7 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
 {
         struct async_struct * info = tty->driver_data;
         unsigned long orig_jiffies, char_time;
+        int tty_was_locked = tty_locked();
         int lsr;
 
         if (serial_paranoia_check(info, tty->name, "rs_wait_until_sent"))
@@ -1538,7 +1539,12 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
 
         orig_jiffies = jiffies;
 
-        tty_lock_nested(); /* tty_wait_until_sent is called from lots of places */
+        /*
+         * tty_wait_until_sent is called from lots of places,
+         * with or without the BTM.
+         */
+        if (!tty_was_locked)
+                tty_lock();
         /*
          * Set the check interval to be 1/5 of the estimated time to
          * send a single character, and make it at least 1.  The check
@@ -1579,7 +1585,8 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
                         break;
         }
         __set_current_state(TASK_RUNNING);
-        tty_unlock();
+        if (!tty_was_locked)
+                tty_unlock();
 #ifdef SERIAL_DEBUG_RS_WAIT_UNTIL_SENT
         printk("lsr = %d (jiff=%lu)...done\n", lsr, jiffies);
 #endif