Drain grouptaskqueue of the gtask before detaching it.

taskqgroup_detach() would remove the task even if it was running or
enqueued, which could lead to panics (see D17404). With this change,
taskqgroup_detach() drains the task and sets a new flag which prevents the
task from being scheduled again.

I've added grouptask_block() and grouptask_unblock() to allow control
over the flag from other locations as well.

Reviewed by:	Jeffrey Pieper <jeffrey.e.pieper@intel.com>
MFC after:	1 week
Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D17674

2 files changed, 58 insertions, 3 deletions

diff --git a/sys/kern/subr_gtaskqueue.c b/sys/kern/subr_gtaskqueue.c
index 96dc530373a3..fb68c1082147 100644
--- a/sys/kern/subr_gtaskqueue.c
+++ b/sys/kern/subr_gtaskqueue.c
@@ -51,6 +51,8 @@ __FBSDID("$FreeBSD$");
 static MALLOC_DEFINE(M_GTASKQUEUE, "gtaskqueue", "Group Task Queues");
 static void	gtaskqueue_thread_enqueue(void *);
 static void	gtaskqueue_thread_loop(void *arg);
+static int	task_is_running(struct gtaskqueue *queue, struct gtask *gtask);
+static void	gtaskqueue_drain_locked(struct gtaskqueue *queue, struct gtask *gtask);
 
 TASKQGROUP_DEFINE(softirq, mp_ncpus, 1);
 TASKQGROUP_DEFINE(config, 1, 1);
@@ -183,6 +185,44 @@ gtaskqueue_free(struct gtaskqueue *queue)
 	free(queue, M_GTASKQUEUE);
 }
 
+/*
+ * Wait for all to complete, then prevent it from being enqueued
+ */
+void
+grouptask_block(struct grouptask *grouptask)
+{
+	struct gtaskqueue *queue = grouptask->gt_taskqueue;
+	struct gtask *gtask = &grouptask->gt_task;
+
+#ifdef INVARIANTS
+	if (queue == NULL) {
+		gtask_dump(gtask);
+		panic("queue == NULL");
+	}
+#endif
+	TQ_LOCK(queue);
+	gtask->ta_flags |= TASK_NOENQUEUE;
+  	gtaskqueue_drain_locked(queue, gtask);
+	TQ_UNLOCK(queue);
+}
+
+void
+grouptask_unblock(struct grouptask *grouptask)
+{
+	struct gtaskqueue *queue = grouptask->gt_taskqueue;
+	struct gtask *gtask = &grouptask->gt_task;
+
+#ifdef INVARIANTS
+	if (queue == NULL) {
+		gtask_dump(gtask);
+		panic("queue == NULL");
+	}
+#endif
+	TQ_LOCK(queue);
+	gtask->ta_flags &= ~TASK_NOENQUEUE;
+	TQ_UNLOCK(queue);
+}
+
 int
 grouptaskqueue_enqueue(struct gtaskqueue *queue, struct gtask *gtask)
 {
@@ -197,6 +237,10 @@ grouptaskqueue_enqueue(struct gtaskqueue *queue, struct gtask *gtask)
 		TQ_UNLOCK(queue);
 		return (0);
 	}
+	if (gtask->ta_flags & TASK_NOENQUEUE) {
+		TQ_UNLOCK(queue);
+		return (EAGAIN);
+	}
 	STAILQ_INSERT_TAIL(&queue->tq_queue, gtask, ta_link);
 	gtask->ta_flags |= TASK_ENQUEUED;
 	TQ_UNLOCK(queue);
@@ -378,6 +422,13 @@ gtaskqueue_cancel(struct gtaskqueue *queue, struct gtask *gtask)
 	return (error);
 }
 
+static void
+gtaskqueue_drain_locked(struct gtaskqueue *queue, struct gtask *gtask)
+{
+	while ((gtask->ta_flags & TASK_ENQUEUED) || task_is_running(queue, gtask))
+		TQ_SLEEP(queue, gtask, &queue->tq_mutex, PWAIT, "-", 0);
+}
+
 void
 gtaskqueue_drain(struct gtaskqueue *queue, struct gtask *gtask)
 {
@@ -386,8 +437,7 @@ gtaskqueue_drain(struct gtaskqueue *queue, struct gtask *gtask)
 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
 
 	TQ_LOCK(queue);
-	while ((gtask->ta_flags & TASK_ENQUEUED) || task_is_running(queue, gtask))
-		TQ_SLEEP(queue, gtask, &queue->tq_mutex, PWAIT, "-", 0);
+	gtaskqueue_drain_locked(queue, gtask);
 	TQ_UNLOCK(queue);
 }
 
@@ -803,6 +853,7 @@ taskqgroup_detach(struct taskqgroup *qgroup, struct grouptask *gtask)
 {
 	int i;
 
+	grouptask_block(gtask);
 	mtx_lock(&qgroup->tqg_lock);
 	for (i = 0; i < qgroup->tqg_cnt; i++)
 		if (qgroup->tqg_queue[i].tgc_taskq == gtask->gt_taskqueue)
@@ -813,6 +864,7 @@ taskqgroup_detach(struct taskqgroup *qgroup, struct grouptask *gtask)
 	LIST_REMOVE(gtask, gt_list);
 	mtx_unlock(&qgroup->tqg_lock);
 	gtask->gt_taskqueue = NULL;
+	gtask->gt_task.ta_flags &= ~TASK_NOENQUEUE;
 }
 
 static void
diff --git a/sys/sys/gtaskqueue.h b/sys/sys/gtaskqueue.h
index c06ef503c11e..a36c770adb97 100644
--- a/sys/sys/gtaskqueue.h
+++ b/sys/sys/gtaskqueue.h
@@ -52,7 +52,9 @@ int	gtaskqueue_cancel(struct gtaskqueue *queue, struct gtask *gtask);
 void	gtaskqueue_drain(struct gtaskqueue *queue, struct gtask *task);
 void	gtaskqueue_drain_all(struct gtaskqueue *queue);
 
-int grouptaskqueue_enqueue(struct gtaskqueue *queue, struct gtask *task);
+void	grouptask_block(struct grouptask *grouptask);
+void	grouptask_unblock(struct grouptask *grouptask);
+int	grouptaskqueue_enqueue(struct gtaskqueue *queue, struct gtask *task);
 void	taskqgroup_attach(struct taskqgroup *qgroup, struct grouptask *grptask,
 	    void *uniq, int irq, const char *name);
 int		taskqgroup_attach_cpu(struct taskqgroup *qgroup, struct grouptask *grptask,
@@ -67,6 +69,7 @@ void	taskqgroup_config_gtask_deinit(struct grouptask *gtask);
 
 #define TASK_ENQUEUED			0x1
 #define TASK_SKIP_WAKEUP		0x2
+#define TASK_NOENQUEUE			0x4
 
 
 #define GTASK_INIT(task, flags, priority, func, context) do {	\