kthread_worker: reimplement flush_kthread_work() to allow freeing the work item being executed
commit 46f3d976213452350f9d10b0c2780c2681f7075b upstream.
kthread_worker provides minimalistic workqueue-like interface for
users which need a dedicated worker thread (e.g. for realtime
priority). It has basic queue, flush_work, flush_worker operations
which mostly match the workqueue counterparts; however, due to the way
flush_work() is implemented, it has a noticeable difference of not
allowing work items to be freed while being executed.
While the current users of kthread_worker are okay with the current
behavior, the restriction does impede some valid use cases. Also,
removing this difference isn't difficult and actually makes the code
easier to understand.
This patch reimplements flush_kthread_work() such that it uses a
flush_work item instead of queue/done sequence numbers.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Colin Cross <ccross@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 0714b24..22ccf9d 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -49,8 +49,6 @@
* can be queued and flushed using queue/flush_kthread_work()
* respectively. Queued kthread_works are processed by a kthread
* running kthread_worker_fn().
- *
- * A kthread_work can't be freed while it is executing.
*/
struct kthread_work;
typedef void (*kthread_work_func_t)(struct kthread_work *work);
@@ -59,15 +57,14 @@
spinlock_t lock;
struct list_head work_list;
struct task_struct *task;
+ struct kthread_work *current_work;
};
struct kthread_work {
struct list_head node;
kthread_work_func_t func;
wait_queue_head_t done;
- atomic_t flushing;
- int queue_seq;
- int done_seq;
+ struct kthread_worker *worker;
};
#define KTHREAD_WORKER_INIT(worker) { \
@@ -79,7 +76,6 @@
.node = LIST_HEAD_INIT((work).node), \
.func = (fn), \
.done = __WAIT_QUEUE_HEAD_INITIALIZER((work).done), \
- .flushing = ATOMIC_INIT(0), \
}
#define DEFINE_KTHREAD_WORKER(worker) \
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 4bfbff3..b579af5 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -360,16 +360,12 @@
struct kthread_work, node);
list_del_init(&work->node);
}
+ worker->current_work = work;
spin_unlock_irq(&worker->lock);
if (work) {
__set_current_state(TASK_RUNNING);
work->func(work);
- smp_wmb(); /* wmb worker-b0 paired with flush-b1 */
- work->done_seq = work->queue_seq;
- smp_mb(); /* mb worker-b1 paired with flush-b0 */
- if (atomic_read(&work->flushing))
- wake_up_all(&work->done);
} else if (!freezing(current))
schedule();
@@ -386,7 +382,7 @@
lockdep_assert_held(&worker->lock);
list_add_tail(&work->node, pos);
- work->queue_seq++;
+ work->worker = worker;
if (likely(worker->task))
wake_up_process(worker->task);
}
@@ -436,25 +432,35 @@
*/
void flush_kthread_work(struct kthread_work *work)
{
- int seq = work->queue_seq;
+ struct kthread_flush_work fwork = {
+ KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+ COMPLETION_INITIALIZER_ONSTACK(fwork.done),
+ };
+ struct kthread_worker *worker;
+ bool noop = false;
- atomic_inc(&work->flushing);
+retry:
+ worker = work->worker;
+ if (!worker)
+ return;
- /*
- * mb flush-b0 paired with worker-b1, to make sure either
- * worker sees the above increment or we see done_seq update.
- */
- smp_mb__after_atomic_inc();
+ spin_lock_irq(&worker->lock);
+ if (work->worker != worker) {
+ spin_unlock_irq(&worker->lock);
+ goto retry;
+ }
- /* A - B <= 0 tests whether B is in front of A regardless of overflow */
- wait_event(work->done, seq - work->done_seq <= 0);
- atomic_dec(&work->flushing);
+ if (!list_empty(&work->node))
+ insert_kthread_work(worker, &fwork.work, work->node.next);
+ else if (worker->current_work == work)
+ insert_kthread_work(worker, &fwork.work, worker->work_list.next);
+ else
+ noop = true;
- /*
- * rmb flush-b1 paired with worker-b0, to make sure our caller
- * sees every change made by work->func().
- */
- smp_mb__after_atomic_dec();
+ spin_unlock_irq(&worker->lock);
+
+ if (!noop)
+ wait_for_completion(&fwork.done);
}
EXPORT_SYMBOL_GPL(flush_kthread_work);