drbd: allow to dequeue batches of work at a time

cherry-picked and adapted from drbd 9 devel branch

In 8.4, we still use drbd_queue_work_front(),
so in normal operation, we can not dequeue batches,
but only single items.

Still, followup commits will wake the worker
without explicitly queueing a work item,
so up() is replaced by a simple wake_up().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

3 files changed, 43 insertions, 55 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index d7ca76ce00cb..e84c7b6a6bac 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -735,8 +735,8 @@ enum bm_flag {
 
 struct drbd_work_queue {
         struct list_head q;
-        struct semaphore s; /* producers up it, worker down()s it */
         spinlock_t q_lock;  /* to protect the list. */
+        wait_queue_head_t q_wait;
 };
 
 struct drbd_socket {
@@ -1832,9 +1832,8 @@ drbd_queue_work_front(struct drbd_work_queue *q, struct drbd_work *w)
         unsigned long flags;
         spin_lock_irqsave(&q->q_lock, flags);
         list_add(&w->list, &q->q);
-        up(&q->s); /* within the spinlock,
-                      see comment near end of drbd_worker() */
         spin_unlock_irqrestore(&q->q_lock, flags);
+        wake_up(&q->q_wait);
 }
 
 static inline void
@@ -1843,9 +1842,8 @@ drbd_queue_work(struct drbd_work_queue *q, struct drbd_work *w)
         unsigned long flags;
         spin_lock_irqsave(&q->q_lock, flags);
         list_add_tail(&w->list, &q->q);
-        up(&q->s); /* within the spinlock,
-                      see comment near end of drbd_worker() */
         spin_unlock_irqrestore(&q->q_lock, flags);
+        wake_up(&q->q_wait);
 }
 
 static inline void wake_asender(struct drbd_tconn *tconn)
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index bfe6975ef94c..f379d33b10a4 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2535,9 +2535,9 @@ out:
 
 static void drbd_init_workqueue(struct drbd_work_queue* wq)
 {
-        sema_init(&wq->s, 0);
         spin_lock_init(&wq->q_lock);
         INIT_LIST_HEAD(&wq->q);
+        init_waitqueue_head(&wq->q_wait);
 }
 
 struct drbd_tconn *conn_get_by_name(const char *name)
diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index d7573f4b7421..fb2e6c8d45c9 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -1673,6 +1673,23 @@ void drbd_start_resync(struct drbd_conf *mdev, enum drbd_conns side)
         mutex_unlock(mdev->state_mutex);
 }
 
+bool dequeue_work_batch(struct drbd_work_queue *queue, struct list_head *work_list)
+{
+        spin_lock_irq(&queue->q_lock);
+        list_splice_init(&queue->q, work_list);
+        spin_unlock_irq(&queue->q_lock);
+        return !list_empty(work_list);
+}
+
+bool dequeue_work_item(struct drbd_work_queue *queue, struct list_head *work_list)
+{
+        spin_lock_irq(&queue->q_lock);
+        if (!list_empty(&queue->q))
+                list_move(queue->q.next, work_list);
+        spin_unlock_irq(&queue->q_lock);
+        return !list_empty(work_list);
+}
+
 int drbd_worker(struct drbd_thread *thi)
 {
         struct drbd_tconn *tconn = thi->tconn;
@@ -1680,15 +1697,21 @@ int drbd_worker(struct drbd_thread *thi)
         struct drbd_conf *mdev;
         struct net_conf *nc;
         LIST_HEAD(work_list);
-        int vnr, intr = 0;
+        int vnr;
         int cork;
 
         while (get_t_state(thi) == RUNNING) {
                 drbd_thread_current_set_cpu(thi);
 
-                if (down_trylock(&tconn->data.work.s)) {
-                        mutex_lock(&tconn->data.mutex);
+                /* as long as we use drbd_queue_work_front(),
+                 * we may only dequeue single work items here, not batches. */
+                if (list_empty(&work_list))
+                        dequeue_work_item(&tconn->data.work, &work_list);
 
+                /* Still nothing to do? Poke TCP, just in case,
+                 * then wait for new work (or signal). */
+                if (list_empty(&work_list)) {
+                        mutex_lock(&tconn->data.mutex);
                         rcu_read_lock();
                         nc = rcu_dereference(tconn->net_conf);
                         cork = nc ? nc->tcp_cork : 0;
@@ -1698,15 +1721,16 @@ int drbd_worker(struct drbd_thread *thi)
                                 drbd_tcp_uncork(tconn->data.socket);
                         mutex_unlock(&tconn->data.mutex);
 
-                        intr = down_interruptible(&tconn->data.work.s);
+                        wait_event_interruptible(tconn->data.work.q_wait,
+                                dequeue_work_item(&tconn->data.work, &work_list));
 
                         mutex_lock(&tconn->data.mutex);
-                        if (tconn->data.socket  && cork)
+                        if (tconn->data.socket && cork)
                                 drbd_tcp_cork(tconn->data.socket);
                         mutex_unlock(&tconn->data.mutex);
                 }
 
-                if (intr) {
+                if (signal_pending(current)) {
                         flush_signals(current);
                         if (get_t_state(thi) == RUNNING) {
                                 conn_warn(tconn, "Worker got an unexpected signal\n");
@@ -1717,59 +1741,25 @@ int drbd_worker(struct drbd_thread *thi)
 
                 if (get_t_state(thi) != RUNNING)
                         break;
-                /* With this break, we have done a down() but not consumed
-                   the entry from the list. The cleanup code takes care of
-                   this...   */
-
-                w = NULL;
-                spin_lock_irq(&tconn->data.work.q_lock);
-                if (list_empty(&tconn->data.work.q)) {
-                        /* something terribly wrong in our logic.
-                         * we were able to down() the semaphore,
-                         * but the list is empty... doh.
-                         *
-                         * what is the best thing to do now?
-                         * try again from scratch, restarting the receiver,
-                         * asender, whatnot? could break even more ugly,
-                         * e.g. when we are primary, but no good local data.
-                         *
-                         * I'll try to get away just starting over this loop.
-                         */
-                        conn_warn(tconn, "Work list unexpectedly empty\n");
-                        spin_unlock_irq(&tconn->data.work.q_lock);
-                        continue;
-                }
-                w = list_entry(tconn->data.work.q.next, struct drbd_work, list);
-                list_del_init(&w->list);
-                spin_unlock_irq(&tconn->data.work.q_lock);
 
-                if (w->cb(w, tconn->cstate < C_WF_REPORT_PARAMS)) {
-                        /* dev_warn(DEV, "worker: a callback failed! \n"); */
+                while (!list_empty(&work_list)) {
+                        w = list_first_entry(&work_list, struct drbd_work, list);
+                        list_del_init(&w->list);
+                        if (w->cb(w, tconn->cstate < C_WF_REPORT_PARAMS) == 0)
+                                continue;
                         if (tconn->cstate >= C_WF_REPORT_PARAMS)
                                 conn_request_state(tconn, NS(conn, C_NETWORK_FAILURE), CS_HARD);
                 }
         }
 
-        spin_lock_irq(&tconn->data.work.q_lock);
-        while (!list_empty(&tconn->data.work.q)) {
-                list_splice_init(&tconn->data.work.q, &work_list);
-                spin_unlock_irq(&tconn->data.work.q_lock);
-
+        do {
                 while (!list_empty(&work_list)) {
-                        w = list_entry(work_list.next, struct drbd_work, list);
+                        w = list_first_entry(&work_list, struct drbd_work, list);
                         list_del_init(&w->list);
                         w->cb(w, 1);
                 }
-
-                spin_lock_irq(&tconn->data.work.q_lock);
-        }
-        sema_init(&tconn->data.work.s, 0);
-        /* DANGEROUS race: if someone did queue his work within the spinlock,
-         * but up() ed outside the spinlock, we could get an up() on the
-         * semaphore without corresponding list entry.
-         * So don't do that.
-         */
-        spin_unlock_irq(&tconn->data.work.q_lock);
+                dequeue_work_batch(&tconn->data.work, &work_list);
+        } while (!list_empty(&work_list));
 
         rcu_read_lock();
         idr_for_each_entry(&tconn->volumes, mdev, vnr) {