IPoIB: Use dedicated workqueues per interface

During my recent work on the rtnl lock deadlock in the IPoIB driver, I
saw that even once I fixed the apparent races for a single device, as
soon as that device had any children, new races popped up.  It turns
out that this is because no matter how well we protect against races
on a single device, the fact that all devices use the same workqueue,
and flush_workqueue() flushes *everything* from that workqueue, we can
have one device in the middle of a down and holding the rtnl lock and
another totally unrelated device needing to run mcast_restart_task,
which wants the rtnl lock and will loop trying to take it unless is
sees its own FLAG_ADMIN_UP flag go away.  Because the unrelated
interface will never see its own ADMIN_UP flag drop, the interface
going down will deadlock trying to flush the queue.  There are several
possible solutions to this problem:

Make carrier_on_task and mcast_restart_task try to take the rtnl for
some set period of time and if they fail, then bail.  This runs the
real risk of dropping work on the floor, which can end up being its
own separate kind of deadlock.

Set some global flag in the driver that says some device is in the
middle of going down, letting all tasks know to bail.  Again, this can
drop work on the floor.  I suppose if our own ADMIN_UP flag doesn't go
away, then maybe after a few tries on the rtnl lock we can queue our
own task back up as a delayed work and return and avoid dropping work
on the floor that way.  But I'm not 100% convinced that we won't cause
other problems.

Or the method this patch attempts to use, which is when we bring an
interface up, create a workqueue specifically for that interface, so
that when we take it back down, we are flushing only those tasks
associated with our interface.  In addition, keep the global
workqueue, but now limit it to only flush tasks.  In this way, the
flush tasks can always flush the device specific work queues without
having deadlock issues.
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -323,6 +323,7 @@ struct ipoib_dev_priv {
 	struct list_head multicast_list;
 	struct rb_root multicast_tree;
 
+	struct workqueue_struct *wq;
 	struct delayed_work mcast_task;
 	struct work_struct carrier_on_task;
 	struct work_struct flush_light;

drivers/infiniband/ulp/ipoib/ipoib_cm.c

@@ -474,7 +474,7 @@ static int ipoib_cm_req_handler(struct ib_cm_id *cm_id, struct ib_cm_event *even
 	}
 
 	spin_lock_irq(&priv->lock);
-	queue_delayed_work(ipoib_workqueue,
+	queue_delayed_work(priv->wq,
 			   &priv->cm.stale_task, IPOIB_CM_RX_DELAY);
 	/* Add this entry to passive ids list head, but do not re-add it
 	 * if IB_EVENT_QP_LAST_WQE_REACHED has moved it to flush list. */
@@ -576,7 +576,7 @@ void ipoib_cm_handle_rx_wc(struct net_device *dev, struct ib_wc *wc)
 			spin_lock_irqsave(&priv->lock, flags);
 			list_splice_init(&priv->cm.rx_drain_list, &priv->cm.rx_reap_list);
 			ipoib_cm_start_rx_drain(priv);
-			queue_work(ipoib_workqueue, &priv->cm.rx_reap_task);
+			queue_work(priv->wq, &priv->cm.rx_reap_task);
 			spin_unlock_irqrestore(&priv->lock, flags);
 		} else
 			ipoib_warn(priv, "cm recv completion event with wrid %d (> %d)\n",
@@ -603,7 +603,7 @@ void ipoib_cm_handle_rx_wc(struct net_device *dev, struct ib_wc *wc)
 				spin_lock_irqsave(&priv->lock, flags);
 				list_move(&p->list, &priv->cm.rx_reap_list);
 				spin_unlock_irqrestore(&priv->lock, flags);
-				queue_work(ipoib_workqueue, &priv->cm.rx_reap_task);
+				queue_work(priv->wq, &priv->cm.rx_reap_task);
 			}
 			return;
 		}
@@ -827,7 +827,7 @@ void ipoib_cm_handle_tx_wc(struct net_device *dev, struct ib_wc *wc)
 
 		if (test_and_clear_bit(IPOIB_FLAG_INITIALIZED, &tx->flags)) {
 			list_move(&tx->list, &priv->cm.reap_list);
-			queue_work(ipoib_workqueue, &priv->cm.reap_task);
+			queue_work(priv->wq, &priv->cm.reap_task);
 		}
 
 		clear_bit(IPOIB_FLAG_OPER_UP, &tx->flags);
@@ -1255,7 +1255,7 @@ static int ipoib_cm_tx_handler(struct ib_cm_id *cm_id,
 
 		if (test_and_clear_bit(IPOIB_FLAG_INITIALIZED, &tx->flags)) {
 			list_move(&tx->list, &priv->cm.reap_list);
-			queue_work(ipoib_workqueue, &priv->cm.reap_task);
+			queue_work(priv->wq, &priv->cm.reap_task);
 		}
 
 		spin_unlock_irqrestore(&priv->lock, flags);
@@ -1284,7 +1284,7 @@ struct ipoib_cm_tx *ipoib_cm_create_tx(struct net_device *dev, struct ipoib_path
 	tx->dev = dev;
 	list_add(&tx->list, &priv->cm.start_list);
 	set_bit(IPOIB_FLAG_INITIALIZED, &tx->flags);
-	queue_work(ipoib_workqueue, &priv->cm.start_task);
+	queue_work(priv->wq, &priv->cm.start_task);
 	return tx;
 }
 
@@ -1295,7 +1295,7 @@ void ipoib_cm_destroy_tx(struct ipoib_cm_tx *tx)
 	if (test_and_clear_bit(IPOIB_FLAG_INITIALIZED, &tx->flags)) {
 		spin_lock_irqsave(&priv->lock, flags);
 		list_move(&tx->list, &priv->cm.reap_list);
-		queue_work(ipoib_workqueue, &priv->cm.reap_task);
+		queue_work(priv->wq, &priv->cm.reap_task);
 		ipoib_dbg(priv, "Reap connection for gid %pI6\n",
 			  tx->neigh->daddr + 4);
 		tx->neigh = NULL;
@@ -1417,7 +1417,7 @@ void ipoib_cm_skb_too_long(struct net_device *dev, struct sk_buff *skb,
 
 	skb_queue_tail(&priv->cm.skb_queue, skb);
 	if (e)
-		queue_work(ipoib_workqueue, &priv->cm.skb_task);
+		queue_work(priv->wq, &priv->cm.skb_task);
 }
 
 static void ipoib_cm_rx_reap(struct work_struct *work)
@@ -1450,7 +1450,7 @@ static void ipoib_cm_stale_task(struct work_struct *work)
 	}
 
 	if (!list_empty(&priv->cm.passive_ids))
-		queue_delayed_work(ipoib_workqueue,
+		queue_delayed_work(priv->wq,
 				   &priv->cm.stale_task, IPOIB_CM_RX_DELAY);
 	spin_unlock_irq(&priv->lock);
 }

drivers/infiniband/ulp/ipoib/ipoib_ib.c

@@ -655,7 +655,7 @@ void ipoib_reap_ah(struct work_struct *work)
 	__ipoib_reap_ah(dev);
 
 	if (!test_bit(IPOIB_STOP_REAPER, &priv->flags))
-		queue_delayed_work(ipoib_workqueue, &priv->ah_reap_task,
+		queue_delayed_work(priv->wq, &priv->ah_reap_task,
 				   round_jiffies_relative(HZ));
 }
 
@@ -696,7 +696,7 @@ int ipoib_ib_dev_open(struct net_device *dev, int flush)
 	}
 
 	clear_bit(IPOIB_STOP_REAPER, &priv->flags);
-	queue_delayed_work(ipoib_workqueue, &priv->ah_reap_task,
+	queue_delayed_work(priv->wq, &priv->ah_reap_task,
 			   round_jiffies_relative(HZ));
 
 	if (!test_and_set_bit(IPOIB_FLAG_INITIALIZED, &priv->flags))
@@ -881,7 +881,7 @@ int ipoib_ib_dev_stop(struct net_device *dev, int flush)
 	set_bit(IPOIB_STOP_REAPER, &priv->flags);
 	cancel_delayed_work(&priv->ah_reap_task);
 	if (flush)
-		flush_workqueue(ipoib_workqueue);
+		flush_workqueue(priv->wq);
 
 	begin = jiffies;
 

drivers/infiniband/ulp/ipoib/ipoib_main.c

@@ -839,7 +839,7 @@ static void ipoib_set_mcast_list(struct net_device *dev)
 		return;
 	}
 
-	queue_work(ipoib_workqueue, &priv->restart_task);
+	queue_work(priv->wq, &priv->restart_task);
 }
 
 static u32 ipoib_addr_hash(struct ipoib_neigh_hash *htbl, u8 *daddr)
@@ -954,7 +954,7 @@ static void ipoib_reap_neigh(struct work_struct *work)
 	__ipoib_reap_neigh(priv);
 
 	if (!test_bit(IPOIB_STOP_NEIGH_GC, &priv->flags))
-		queue_delayed_work(ipoib_workqueue, &priv->neigh_reap_task,
+		queue_delayed_work(priv->wq, &priv->neigh_reap_task,
 				   arp_tbl.gc_interval);
 }
 
@@ -1133,7 +1133,7 @@ static int ipoib_neigh_hash_init(struct ipoib_dev_priv *priv)
 
 	/* start garbage collection */
 	clear_bit(IPOIB_STOP_NEIGH_GC, &priv->flags);
-	queue_delayed_work(ipoib_workqueue, &priv->neigh_reap_task,
+	queue_delayed_work(priv->wq, &priv->neigh_reap_task,
 			   arp_tbl.gc_interval);
 
 	return 0;
@@ -1293,7 +1293,7 @@ int ipoib_dev_init(struct net_device *dev, struct ib_device *ca, int port)
 	return 0;
 
 out_dev_uninit:
-	ipoib_ib_dev_cleanup();
+	ipoib_ib_dev_cleanup(dev);
 
 out_tx_ring_cleanup:
 	vfree(priv->tx_ring);
@@ -1646,7 +1646,7 @@ static struct net_device *ipoib_add_port(const char *format,
 	/* Stop GC if started before flush */
 	set_bit(IPOIB_STOP_NEIGH_GC, &priv->flags);
 	cancel_delayed_work(&priv->neigh_reap_task);
-	flush_workqueue(ipoib_workqueue);
+	flush_workqueue(priv->wq);
 
 event_failed:
 	ipoib_dev_cleanup(priv->dev);
@@ -1717,7 +1717,7 @@ static void ipoib_remove_one(struct ib_device *device)
 		/* Stop GC */
 		set_bit(IPOIB_STOP_NEIGH_GC, &priv->flags);
 		cancel_delayed_work(&priv->neigh_reap_task);
-		flush_workqueue(ipoib_workqueue);
+		flush_workqueue(priv->wq);
 
 		unregister_netdev(priv->dev);
 		free_netdev(priv->dev);
@@ -1758,8 +1758,13 @@ static int __init ipoib_init_module(void)
 	 * unregister_netdev() and linkwatch_event take the rtnl lock,
 	 * so flush_scheduled_work() can deadlock during device
 	 * removal.
+	 *
+	 * In addition, bringing one device up and another down at the
+	 * same time can deadlock a single workqueue, so we have this
+	 * global fallback workqueue, but we also attempt to open a
+	 * per device workqueue each time we bring an interface up
 	 */
-	ipoib_workqueue = create_singlethread_workqueue("ipoib");
+	ipoib_workqueue = create_singlethread_workqueue("ipoib_flush");
 	if (!ipoib_workqueue) {
 		ret = -ENOMEM;
 		goto err_fs;

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -388,7 +388,7 @@ void ipoib_mcast_carrier_on_task(struct work_struct *work)
 	 * the workqueue while holding the rtnl lock, so loop
 	 * on trylock until either we get the lock or we see
 	 * FLAG_ADMIN_UP go away as that signals that we are bailing
-	 * and can safely ignore the carrier on work
+	 * and can safely ignore the carrier on work.
 	 */
 	while (!rtnl_trylock()) {
 		if (!test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))
@@ -432,15 +432,14 @@ static int ipoib_mcast_join_complete(int status,
 	if (!status) {
 		mcast->backoff = 1;
 		if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
-			queue_delayed_work(ipoib_workqueue,
-					   &priv->mcast_task, 0);
+			queue_delayed_work(priv->wq, &priv->mcast_task, 0);
 
 		/*
-		 * Defer carrier on work to ipoib_workqueue to avoid a
+		 * Defer carrier on work to priv->wq to avoid a
 		 * deadlock on rtnl_lock here.
 		 */
 		if (mcast == priv->broadcast)
-			queue_work(ipoib_workqueue, &priv->carrier_on_task);
+			queue_work(priv->wq, &priv->carrier_on_task);
 	} else {
 		if (mcast->logcount++ < 20) {
 			if (status == -ETIMEDOUT || status == -EAGAIN) {
@@ -465,7 +464,7 @@ static int ipoib_mcast_join_complete(int status,
 	if (status == -ENETRESET)
 		status = 0;
 	if (status && test_bit(IPOIB_MCAST_RUN, &priv->flags))
-		queue_delayed_work(ipoib_workqueue, &priv->mcast_task,
+		queue_delayed_work(priv->wq, &priv->mcast_task,
 				   mcast->backoff * HZ);
 	spin_unlock_irq(&priv->lock);
 	mutex_unlock(&mcast_mutex);
@@ -535,8 +534,7 @@ static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast,
 			mcast->backoff = IPOIB_MAX_BACKOFF_SECONDS;
 
 		if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
-			queue_delayed_work(ipoib_workqueue,
-					   &priv->mcast_task,
+			queue_delayed_work(priv->wq, &priv->mcast_task,
 					   mcast->backoff * HZ);
 	}
 	mutex_unlock(&mcast_mutex);
@@ -576,8 +574,8 @@ void ipoib_mcast_join_task(struct work_struct *work)
 			ipoib_warn(priv, "failed to allocate broadcast group\n");
 			mutex_lock(&mcast_mutex);
 			if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
-				queue_delayed_work(ipoib_workqueue,
-						   &priv->mcast_task, HZ);
+				queue_delayed_work(priv->wq, &priv->mcast_task,
+						   HZ);
 			mutex_unlock(&mcast_mutex);
 			return;
 		}
@@ -644,7 +642,7 @@ int ipoib_mcast_start_thread(struct net_device *dev)
 
 	mutex_lock(&mcast_mutex);
 	if (!test_and_set_bit(IPOIB_MCAST_RUN, &priv->flags))
-		queue_delayed_work(ipoib_workqueue, &priv->mcast_task, 0);
+		queue_delayed_work(priv->wq, &priv->mcast_task, 0);
 	mutex_unlock(&mcast_mutex);
 
 	return 0;
@@ -662,7 +660,7 @@ int ipoib_mcast_stop_thread(struct net_device *dev, int flush)
 	mutex_unlock(&mcast_mutex);
 
 	if (flush)
-		flush_workqueue(ipoib_workqueue);
+		flush_workqueue(priv->wq);
 
 	return 0;
 }
@@ -729,7 +727,7 @@ void ipoib_mcast_send(struct net_device *dev, u8 *daddr, struct sk_buff *skb)
 		__ipoib_mcast_add(dev, mcast);
 		list_add_tail(&mcast->list, &priv->multicast_list);
 		if (!test_and_set_bit(IPOIB_MCAST_RUN, &priv->flags))
-			queue_delayed_work(ipoib_workqueue, &priv->mcast_task, 0);
+			queue_delayed_work(priv->wq, &priv->mcast_task, 0);
 	}
 
 	if (!mcast->ah) {
@@ -944,7 +942,7 @@ void ipoib_mcast_restart_task(struct work_struct *work)
 	 * completes.  So do like the carrier on task and attempt to
 	 * take the rtnl lock, but if we can't before the ADMIN_UP flag
 	 * goes away, then just return and know that the remove list will
-	 * get flushed later by mcast_dev_flush.
+	 * get flushed later by mcast_stop_thread.
 	 */
 	while (!rtnl_trylock()) {
 		if (!test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))

drivers/infiniband/ulp/ipoib/ipoib_verbs.c

@@ -145,10 +145,20 @@ int ipoib_transport_dev_init(struct net_device *dev, struct ib_device *ca)
 	int ret, size;
 	int i;
 
+	/*
+	 * the various IPoIB tasks assume they will never race against
+	 * themselves, so always use a single thread workqueue
+	 */
+	priv->wq = create_singlethread_workqueue("ipoib_wq");
+	if (!priv->wq) {
+		printk(KERN_WARNING "ipoib: failed to allocate device WQ\n");
+		return -ENODEV;
+	}
+
 	priv->pd = ib_alloc_pd(priv->ca);
 	if (IS_ERR(priv->pd)) {
 		printk(KERN_WARNING "%s: failed to allocate PD\n", ca->name);
-		return -ENODEV;
+		goto out_free_wq;
 	}
 
 	priv->mr = ib_get_dma_mr(priv->pd, IB_ACCESS_LOCAL_WRITE);
@@ -242,6 +252,10 @@ int ipoib_transport_dev_init(struct net_device *dev, struct ib_device *ca)
 
 out_free_pd:
 	ib_dealloc_pd(priv->pd);
+
+out_free_wq:
+	destroy_workqueue(priv->wq);
+	priv->wq = NULL;
 	return -ENODEV;
 }
 
@@ -270,6 +284,12 @@ void ipoib_transport_dev_cleanup(struct net_device *dev)
 
 	if (ib_dealloc_pd(priv->pd))
 		ipoib_warn(priv, "ib_dealloc_pd failed\n");
+
+	if (priv->wq) {
+		flush_workqueue(priv->wq);
+		destroy_workqueue(priv->wq);
+		priv->wq = NULL;
+	}
 }
 
 void ipoib_event(struct ib_event_handler *handler,