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: NAlan Cox <alan@redhat.com>
Acked-by: NDave Johnson <djohnson+linux-kernel@sw.starentnetworks.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>