2 files changed, 29 insertions, 27 deletions

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 0714b24c0e45..22ccf9dee177 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -49,8 +49,6 @@ extern int tsk_fork_get_node(struct task_struct *tsk);
  * 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 @@ struct kthread_worker {
         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 @@ struct kthread_work {
         .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 4bfbff36d447..b579af57ea10 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -360,16 +360,12 @@ repeat:
                                         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 @@ static void insert_kthread_work(struct kthread_worker *worker,
         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 @@ static void kthread_flush_work_fn(struct kthread_work *work)
  */
 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;
+
+retry:
+        worker = work->worker;
+        if (!worker)
+                return;
 
-        atomic_inc(&work->flushing);
+        spin_lock_irq(&worker->lock);
+        if (work->worker != worker) {
+                spin_unlock_irq(&worker->lock);
+                goto retry;
+        }
 
-        /*
-         * 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();
+        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;
 
-        /* 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);
+        spin_unlock_irq(&worker->lock);
 
-        /*
-         * rmb flush-b1 paired with worker-b0, to make sure our caller
-         * sees every change made by work->func().
-         */
-        smp_mb__after_atomic_dec();
+        if (!noop)
+                wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(flush_kthread_work);