add taskq_barrier

taskq_barrier guarantees that any task that was running on the taskq
has finished by the time taskq_barrier returns. it is similar to
intr_barrier.

this is needed for use in ifq_barrier as part of an upcoming change.

3 files changed, 45 insertions, 4 deletions

diff --git a/share/man/man9/task_add.9 b/share/man/man9/task_add.9
index 2c50292d4a5..64a68738952 100644
--- a/share/man/man9/task_add.9
+++ b/share/man/man9/task_add.9
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: task_add.9,v 1.16 2015/09/14 15:14:55 schwarze Exp $
+.\"	$OpenBSD: task_add.9,v 1.17 2017/11/13 23:52:49 dlg Exp $
 .\"
 .\" Copyright (c) 2013 David Gwynne <dlg@openbsd.org>
 .\"
@@ -14,12 +14,13 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: September 14 2015 $
+.Dd $Mdocdate: November 13 2017 $
 .Dt TASK_ADD 9
 .Os
 .Sh NAME
 .Nm taskq_create ,
 .Nm taskq_destroy ,
+.Nm taskq_barrier ,
 .Nm task_set ,
 .Nm task_add ,
 .Nm task_del ,
@@ -37,6 +38,8 @@
 .Ft void
 .Fn taskq_destroy "struct taskq *tq"
 .Ft void
+.Fn taskq_barrier "struct taskq *tq"
+.Ft void
 .Fn task_set "struct task *t" "void (*fn)(void *)" "void *arg"
 .Ft int
 .Fn task_add "struct taskq *tq" "struct task *t"
@@ -88,6 +91,15 @@ Calling
 against the system taskq is an error and will lead to undefined
 behaviour or a system fault.
 .Pp
+.Fn taskq_barrier
+guarantees that any task that was running on the
+.Fa tq
+taskq when the barrier was called has finished by the time the barrier
+returns.
+.Fn taskq_barrier
+is only supported on taskqs serviced by 1 thread,
+and may not be called by a task running in the specified taskq.
+.Pp
 It is the responsibility of the caller to provide the
 .Fn task_set ,
 .Fn task_add ,
@@ -163,6 +175,8 @@ argument given in
 and
 .Fn taskq_destroy
 can be called during autoconf, or from process context.
+.Fn taskq_barrier
+can be called from process context.
 .Fn task_set ,
 .Fn task_add ,
 and
diff --git a/sys/kern/kern_task.c b/sys/kern/kern_task.c
index cd7e2a436f4..feaa7bed5cd 100644
--- a/sys/kern/kern_task.c
+++ b/sys/kern/kern_task.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_task.c,v 1.20 2017/10/30 14:01:42 visa Exp $ */
+/*	$OpenBSD: kern_task.c,v 1.21 2017/11/13 23:52:49 dlg Exp $ */
 
 /*
  * Copyright (c) 2013 David Gwynne <dlg@openbsd.org>
@@ -22,6 +22,7 @@
 #include <sys/mutex.h>
 #include <sys/kthread.h>
 #include <sys/task.h>
+#include <sys/proc.h>
 
 #define TASK_ONQUEUE	1
 
@@ -68,6 +69,7 @@ struct taskq *const systqmp = &taskq_sys_mp;
 
 void	taskq_init(void); /* called in init_main.c */
 void	taskq_create_thread(void *);
+void	taskq_barrier_task(void *);
 int	taskq_sleep(const volatile void *, struct mutex *, int,
 	    const char *, int);
 int	taskq_next_work(struct taskq *, struct task *, sleepfn);
@@ -179,6 +181,30 @@ taskq_create_thread(void *arg)
 }
 
 void
+taskq_barrier(struct taskq *tq)
+{
+	struct sleep_state sls;
+	unsigned int notdone = 1;
+	struct task t = TASK_INITIALIZER(taskq_barrier_task, &notdone);
+
+	task_add(tq, &t);
+
+	while (notdone) {
+		sleep_setup(&sls, &notdone, PWAIT, "tqbar");
+		sleep_finish(&sls, notdone);
+	}
+}
+
+void
+taskq_barrier_task(void *p)
+{
+	unsigned int *notdone = p;
+
+	*notdone = 0;
+	wakeup_one(notdone);
+}
+
+void
 task_set(struct task *t, void (*fn)(void *), void *arg)
 {
 	t->t_func = fn;
diff --git a/sys/sys/task.h b/sys/sys/task.h
index 1db033a0f0c..f7385ca0cfd 100644
--- a/sys/sys/task.h
+++ b/sys/sys/task.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: task.h,v 1.11 2016/06/07 07:53:33 mpi Exp $ */
+/*	$OpenBSD: task.h,v 1.12 2017/11/13 23:52:49 dlg Exp $ */
 
 /*
  * Copyright (c) 2013 David Gwynne <dlg@openbsd.org>
@@ -43,6 +43,7 @@ extern struct taskq *const systqmp;
 
 struct taskq	*taskq_create(const char *, unsigned int, int, unsigned int);
 void		 taskq_destroy(struct taskq *);
+void		 taskq_barrier(struct taskq *);
 
 void		 task_set(struct task *, void (*)(void *), void *);
 int		 task_add(struct taskq *, struct task *);