Prevent an O_NDELAY writer from blocking when a tty write is blocked by the tty atomic writer mutex

Without this a tty write could block if a previous blocking tty write was
in progress on the same tty and blocked by a line discipline or hardware
event.  Originally found and reported by Dave Johnson.

Signed-off-by: Alan Cox <alan@redhat.com>
Acked-by: Dave Johnson <djohnson+linux-kernel@sw.starentnetworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index fd471cb3338f..918e24c885f1 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -667,7 +667,7 @@ static int send_prio_char(struct tty_struct *tty, char ch)
                 return 0;
         }
 
-        if (mutex_lock_interruptible(&tty->atomic_write_lock))
+        if (tty_write_lock(tty, 0) < 0)
                 return -ERESTARTSYS;
 
         if (was_stopped)
@@ -675,7 +675,7 @@ static int send_prio_char(struct tty_struct *tty, char ch)
         tty->driver->write(tty, &ch, 1);
         if (was_stopped)
                 stop_tty(tty);
-        mutex_unlock(&tty->atomic_write_lock);
+        tty_write_unlock(tty);
         return 0;
 }