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While draining a timeout task prevent the taskqueue_enqueue_timeout()

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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
This commit is contained in:
Hans Petter Selasky 2016-09-29 10:38:20 +00:00
parent c5072d5c94
commit 99eca1b2b3
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=306441
2 changed files with 24 additions and 1 deletions
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2
share/man/man9/taskqueue.9
View File

@ -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

23
sys/kern/subr_taskqueue.c
View File

@ -81,6 +81,7 @@ struct taskqueue {
#define TQ_FLAGS_UNLOCKED_ENQUEUE (1 << 2)
#define DT_CALLOUT_ARMED (1 << 0)
#define DT_DRAIN_IN_PROGRESS (1 << 1)
#define TQ_LOCK(tq) \
do { \
@ -299,7 +300,11 @@ taskqueue_enqueue_timeout(struct taskqueue *queue,
KASSERT(!queue->tq_spin, ("Timeout for spin-queue"));
timeout_task->q = queue;
res = timeout_task->t.ta_pending;
if (ticks == 0) {
if (timeout_task->f & DT_DRAIN_IN_PROGRESS) {
/* Do nothing */
TQ_UNLOCK(queue);
res = -1;
} else if (ticks == 0) {
taskqueue_enqueue_locked(queue, &timeout_task->t);
/* The lock is released inside. */
} else {
@ -559,8 +564,24 @@ taskqueue_drain_timeout(struct taskqueue *queue,
struct timeout_task *timeout_task)
{
/*
* Set flag to prevent timer from re-starting during drain:
*/
TQ_LOCK(queue);
KASSERT((timeout_task->f & DT_DRAIN_IN_PROGRESS) == 0,
("Drain already in progress"));
timeout_task->f |= DT_DRAIN_IN_PROGRESS;
TQ_UNLOCK(queue);
callout_drain(&timeout_task->c);
taskqueue_drain(queue, &timeout_task->t);
/*
* Clear flag to allow timer to re-start:
*/
TQ_LOCK(queue);
timeout_task->f &= ~DT_DRAIN_IN_PROGRESS;
TQ_UNLOCK(queue);
}
static void