While draining a timeout task prevent the taskqueue_enqueue_timeout()

function from restarting the timer.

Commonly taskqueue_enqueue_timeout() is called from within the task
function itself without any checks for teardown. Then it can happen
the timer stays active after the return of taskqueue_drain_timeout(),
because the timeout and task is drained separately.

This patch factors out the teardown flag into the timeout task itself,
allowing existing code to stay as-is instead of applying a teardown
flag to each and every of the timeout task consumers.

Add assert to taskqueue_drain_timeout() which prevents parallel
execution on the same timeout task.

Update manual page documenting the return value of
taskqueue_enqueue_timeout().

Differential Revision:	https://reviews.freebsd.org/D8012
Reviewed by:	kib, trasz
MFC after:	1 week

1 files changed, 2 insertions, 0 deletions

diff --git a/share/man/man9/taskqueue.9 b/share/man/man9/taskqueue.9
index 5ee7fc8b36a4..2d39eee91796 100644
--- a/share/man/man9/taskqueue.9
+++ b/share/man/man9/taskqueue.9
@@ -223,6 +223,8 @@ Otherwise, the task is scheduled for enqueueing in the future,
 after the absolute value of
 .Va ticks
 is passed.
+This function will return -1 if the queue is being drained.
+Otherwise the number of pending calls will be returned.
 .Pp
 The
 .Fn taskqueue_cancel