svn commit: r276665 - in head: share/man/man9 sys/kern
Justin T. Gibbs
gibbs at FreeBSD.org
Sun Jan 4 19:55:46 UTC 2015
Author: gibbs
Date: Sun Jan 4 19:55:44 2015
New Revision: 276665
URL: https://svnweb.freebsd.org/changeset/base/276665
Log:
Prevent live-lock and access of destroyed data in taskqueue_drain_all().
Phabric: https://reviews.freebsd.org/D1247
Reviewed by: jhb, avg
Sponsored by: Spectra Logic Corporation
sys/kern_subr_taskqueue.c:
Modify taskqueue_drain_all() processing to use a temporary
"barrier task", rather than rely on a user task that may
be destroyed during taskqueue_drain_all()'s execution. The
barrier task is queued behind all previously queued tasks
and then has its priority elevated so that future tasks
cannot pass it in the queue.
Use a similar barrier scheme to drain threads processing
current tasks. This requires taskqueue_run_locked() to
insert and remove the taskqueue_busy object for the running
thread for every task processed.
share/man/man9/taskqueue.9:
Remove warning about live-lock issues with taskqueue_drain_all()
and indicate that it does not wait for tasks queued after
it begins processing.
Modified:
head/share/man/man9/taskqueue.9
head/sys/kern/subr_taskqueue.c
Modified: head/share/man/man9/taskqueue.9
==============================================================================
--- head/share/man/man9/taskqueue.9 Sun Jan 4 19:05:16 2015 (r276664)
+++ head/share/man/man9/taskqueue.9 Sun Jan 4 19:55:44 2015 (r276665)
@@ -28,7 +28,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd May 24, 2014
+.Dd January 4, 2015
.Dt TASKQUEUE 9
.Os
.Sh NAME
@@ -285,10 +285,16 @@ The
.Fn taskqueue_drain_all
function is used to wait for all pending and running tasks that
are enqueued on the taskqueue to finish.
-The caller must arrange that the tasks are not re-enqueued.
-Note that
+Tasks posted to the taskqueue after
.Fn taskqueue_drain_all
-currently does not handle tasks with delayed enqueueing.
+begins processing,
+including pending enqueues scheduled by a previous call to
+.Fn taskqueue_enqueue_timeout ,
+do not extend the wait time of
+.Fn taskqueue_drain_all
+and may complete after
+.Fn taskqueue_drain_all
+returns.
.Pp
The
.Fn taskqueue_block
Modified: head/sys/kern/subr_taskqueue.c
==============================================================================
--- head/sys/kern/subr_taskqueue.c Sun Jan 4 19:05:16 2015 (r276664)
+++ head/sys/kern/subr_taskqueue.c Sun Jan 4 19:55:44 2015 (r276665)
@@ -56,6 +56,8 @@ struct taskqueue_busy {
TAILQ_ENTRY(taskqueue_busy) tb_link;
};
+struct task * const TB_DRAIN_WAITER = (struct task *)0x1;
+
struct taskqueue {
STAILQ_HEAD(, task) tq_queue;
taskqueue_enqueue_fn tq_enqueue;
@@ -241,6 +243,7 @@ taskqueue_enqueue_locked(struct taskqueu
/* Return with lock released. */
return (0);
}
+
int
taskqueue_enqueue(struct taskqueue *queue, struct task *task)
{
@@ -302,12 +305,82 @@ taskqueue_enqueue_timeout(struct taskque
}
static void
-taskqueue_drain_running(struct taskqueue *queue)
+taskqueue_task_nop_fn(void *context, int pending)
+{
+}
+
+/*
+ * Block until all currently queued tasks in this taskqueue
+ * have begun execution. Tasks queued during execution of
+ * this function are ignored.
+ */
+static void
+taskqueue_drain_tq_queue(struct taskqueue *queue)
{
+ struct task t_barrier;
- while (!TAILQ_EMPTY(&queue->tq_active))
- TQ_SLEEP(queue, &queue->tq_active, &queue->tq_mutex,
- PWAIT, "-", 0);
+ if (STAILQ_EMPTY(&queue->tq_queue))
+ return;
+
+ /*
+ * Enqueue our barrier with the lowest possible priority
+ * so we are inserted after all current tasks.
+ */
+ TASK_INIT(&t_barrier, 0, taskqueue_task_nop_fn, &t_barrier);
+ taskqueue_enqueue_locked(queue, &t_barrier);
+
+ /*
+ * Raise the barrier's priority so newly queued tasks cannot
+ * pass it.
+ */
+ t_barrier.ta_priority = USHRT_MAX;
+
+ /*
+ * Once the barrier has executed, all previously queued tasks
+ * have completed or are currently executing.
+ */
+ while (t_barrier.ta_pending != 0)
+ TQ_SLEEP(queue, &t_barrier, &queue->tq_mutex, PWAIT, "-", 0);
+}
+
+/*
+ * Block until all currently executing tasks for this taskqueue
+ * complete. Tasks that begin execution during the execution
+ * of this function are ignored.
+ */
+static void
+taskqueue_drain_tq_active(struct taskqueue *queue)
+{
+ struct taskqueue_busy tb_marker, *tb_first;
+
+ if (TAILQ_EMPTY(&queue->tq_active))
+ return;
+
+ /* Block taskq_terminate().*/
+ queue->tq_callouts++;
+
+ /*
+ * Wait for all currently executing taskqueue threads
+ * to go idle.
+ */
+ tb_marker.tb_running = TB_DRAIN_WAITER;
+ TAILQ_INSERT_TAIL(&queue->tq_active, &tb_marker, tb_link);
+ while (TAILQ_FIRST(&queue->tq_active) != &tb_marker)
+ TQ_SLEEP(queue, &tb_marker, &queue->tq_mutex, PWAIT, "-", 0);
+ TAILQ_REMOVE(&queue->tq_active, &tb_marker, tb_link);
+
+ /*
+ * Wakeup any other drain waiter that happened to queue up
+ * without any intervening active thread.
+ */
+ tb_first = TAILQ_FIRST(&queue->tq_active);
+ if (tb_first != NULL && tb_first->tb_running == TB_DRAIN_WAITER)
+ wakeup(tb_first);
+
+ /* Release taskqueue_terminate(). */
+ queue->tq_callouts--;
+ if ((queue->tq_flags & TQ_FLAGS_ACTIVE) == 0)
+ wakeup_one(queue->tq_threads);
}
void
@@ -334,14 +407,16 @@ static void
taskqueue_run_locked(struct taskqueue *queue)
{
struct taskqueue_busy tb;
+ struct taskqueue_busy *tb_first;
struct task *task;
int pending;
TQ_ASSERT_LOCKED(queue);
tb.tb_running = NULL;
- TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
while (STAILQ_FIRST(&queue->tq_queue)) {
+ TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
+
/*
* Carefully remove the first task from the queue and
* zero its pending count.
@@ -358,10 +433,13 @@ taskqueue_run_locked(struct taskqueue *q
TQ_LOCK(queue);
tb.tb_running = NULL;
wakeup(task);
+
+ TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
+ tb_first = TAILQ_FIRST(&queue->tq_active);
+ if (tb_first != NULL &&
+ tb_first->tb_running == TB_DRAIN_WAITER)
+ wakeup(tb_first);
}
- TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
- if (TAILQ_EMPTY(&queue->tq_active))
- wakeup(&queue->tq_active);
}
void
@@ -448,19 +526,13 @@ taskqueue_drain(struct taskqueue *queue,
void
taskqueue_drain_all(struct taskqueue *queue)
{
- struct task *task;
if (!queue->tq_spin)
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
TQ_LOCK(queue);
- task = STAILQ_LAST(&queue->tq_queue, task, ta_link);
- if (task != NULL)
- while (task->ta_pending != 0)
- TQ_SLEEP(queue, task, &queue->tq_mutex, PWAIT, "-", 0);
- taskqueue_drain_running(queue);
- KASSERT(STAILQ_EMPTY(&queue->tq_queue),
- ("taskqueue queue is not empty after draining"));
+ taskqueue_drain_tq_queue(queue);
+ taskqueue_drain_tq_active(queue);
TQ_UNLOCK(queue);
}
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