IPoIB: fix MCAST_FLAG_BUSY usage

Commit a9c8ba5884 ("IPoIB: Fix usage of uninitialized multicast
objects") added a new flag MCAST_JOIN_STARTED, but was not very strict
in how it was used.  We didn't always initialize the completion struct
before we set the flag, and we didn't always call complete on the
completion struct from all paths that complete it.  This made it less
than totally effective, and certainly made its use confusing.  And in
the flush function we would use the presence of this flag to signal
that we should wait on the completion struct, but we never cleared
this flag, ever.  This is further muddied by the fact that we overload
the MCAST_FLAG_BUSY flag to mean two different things: we have a join
in flight, and we have succeeded in getting an ib_sa_join_multicast.

In order to make things clearer and aid in resolving the rtnl deadlock
bug I've been chasing, I cleaned this up a bit.

 1) Remove the MCAST_JOIN_STARTED flag entirely
 2) Un-overload MCAST_FLAG_BUSY so it now only means a join is in-flight
 3) Test on mcast->mc directly to see if we have completed
    ib_sa_join_multicast (using IS_ERR_OR_NULL)
 4) Make sure that before setting MCAST_FLAG_BUSY we always initialize
    the mcast->done completion struct
 5) Make sure that before calling complete(&mcast->done), we always clear
    the MCAST_FLAG_BUSY bit
 6) Take the mcast_mutex before we call ib_sa_multicast_join and also
    take the mutex in our join callback.  This forces
    ib_sa_multicast_join to return and set mcast->mc before we process
    the callback.  This way, our callback can safely clear mcast->mc
    if there is an error on the join and we will do the right thing as
    a result in mcast_dev_flush.
 7) Because we need the mutex to synchronize mcast->mc, we can no
    longer call mcast_sendonly_join directly from mcast_send and
    instead must add sendonly join processing to the mcast_join_task

A number of different races are resolved with these changes.  These
races existed with the old MCAST_FLAG_BUSY usage, the
MCAST_JOIN_STARTED flag was an attempt to address them, and while it
helped, a determined effort could still trip things up.

One race looks something like this:

Thread 1                             Thread 2
ib_sa_join_multicast (as part of running restart mcast task)
  alloc member
  call callback
                                     ifconfig ib0 down
				     wait_for_completion
    callback call completes
                                     wait_for_completion in
				     mcast_dev_flush completes
				       mcast->mc is PTR_ERR_OR_NULL
				       so we skip ib_sa_leave_multicast
    return from callback
  return from ib_sa_join_multicast
set mcast->mc = return from ib_sa_multicast

We now have a permanently unbalanced join/leave issue that trips up the
refcounting in core/multicast.c

Another like this:

Thread 1                   Thread 2         Thread 3
ib_sa_multicast_join
                                            ifconfig ib0 down
					    priv->broadcast = NULL
                           join_complete
			                    wait_for_completion
			   mcast->mc is not yet set, so don't clear
return from ib_sa_join_multicast and set mcast->mc
			   complete
			   return -EAGAIN (making mcast->mc invalid)
			   		    call ib_sa_multicast_leave
					    on invalid mcast->mc, hang
					    forever

By holding the mutex around ib_sa_multicast_join and taking the mutex
early in the callback, we force mcast->mc to be valid at the time we
run the callback.  This allows us to clear mcast->mc if there is an
error and the join is going to fail.  We do this before we complete
the mcast.  In this way, mcast_dev_flush always sees consistent state
in regards to mcast->mc membership at the time that the
wait_for_completion() returns.

Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -98,9 +98,15 @@ enum {
 
 	IPOIB_MCAST_FLAG_FOUND	  = 0,	/* used in set_multicast_list */
 	IPOIB_MCAST_FLAG_SENDONLY = 1,
-	IPOIB_MCAST_FLAG_BUSY	  = 2,	/* joining or already joined */
+	/*
+	 * For IPOIB_MCAST_FLAG_BUSY
+	 * When set, in flight join and mcast->mc is unreliable
+	 * When clear and mcast->mc IS_ERR_OR_NULL, need to restart or
+	 *   haven't started yet
+	 * When clear and mcast->mc is valid pointer, join was successful
+	 */
+	IPOIB_MCAST_FLAG_BUSY	  = 2,
 	IPOIB_MCAST_FLAG_ATTACHED = 3,
-	IPOIB_MCAST_JOIN_STARTED  = 4,
 
 	MAX_SEND_CQE		  = 16,
 	IPOIB_CM_COPYBREAK	  = 256,

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -271,16 +271,27 @@ ipoib_mcast_sendonly_join_complete(int status,
 	struct ipoib_mcast *mcast = multicast->context;
 	struct net_device *dev = mcast->dev;
 
+	/*
+	 * We have to take the mutex to force mcast_sendonly_join to
+	 * return from ib_sa_multicast_join and set mcast->mc to a
+	 * valid value.  Otherwise we were racing with ourselves in
+	 * that we might fail here, but get a valid return from
+	 * ib_sa_multicast_join after we had cleared mcast->mc here,
+	 * resulting in mis-matched joins and leaves and a deadlock
+	 */
+	mutex_lock(&mcast_mutex);
+
 	/* We trap for port events ourselves. */
 	if (status == -ENETRESET)
-		return 0;
+		goto out;
 
 	if (!status)
 		status = ipoib_mcast_join_finish(mcast, &multicast->rec);
 
 	if (status) {
 		if (mcast->logcount++ < 20)
-			ipoib_dbg_mcast(netdev_priv(dev), "multicast join failed for %pI6, status %d\n",
+			ipoib_dbg_mcast(netdev_priv(dev), "sendonly multicast "
+					"join failed for %pI6, status %d\n",
 					mcast->mcmember.mgid.raw, status);
 
 		/* Flush out any queued packets */
@@ -290,11 +301,15 @@ ipoib_mcast_sendonly_join_complete(int status,
 			dev_kfree_skb_any(skb_dequeue(&mcast->pkt_queue));
 		}
 		netif_tx_unlock_bh(dev);
-
-		/* Clear the busy flag so we try again */
-		status = test_and_clear_bit(IPOIB_MCAST_FLAG_BUSY,
-					    &mcast->flags);
 	}
+out:
+	clear_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
+	if (status)
+		mcast->mc = NULL;
+	complete(&mcast->done);
+	if (status == -ENETRESET)
+		status = 0;
+	mutex_unlock(&mcast_mutex);
 	return status;
 }
 
@@ -312,12 +327,14 @@ static int ipoib_mcast_sendonly_join(struct ipoib_mcast *mcast)
 	int ret = 0;
 
 	if (!test_bit(IPOIB_FLAG_OPER_UP, &priv->flags)) {
-		ipoib_dbg_mcast(priv, "device shutting down, no multicast joins\n");
+		ipoib_dbg_mcast(priv, "device shutting down, no sendonly "
+				"multicast joins\n");
 		return -ENODEV;
 	}
 
-	if (test_and_set_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags)) {
-		ipoib_dbg_mcast(priv, "multicast entry busy, skipping\n");
+	if (test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags)) {
+		ipoib_dbg_mcast(priv, "multicast entry busy, skipping "
+				"sendonly join\n");
 		return -EBUSY;
 	}
 
@@ -325,6 +342,9 @@ static int ipoib_mcast_sendonly_join(struct ipoib_mcast *mcast)
 	rec.port_gid = priv->local_gid;
 	rec.pkey     = cpu_to_be16(priv->pkey);
 
+	mutex_lock(&mcast_mutex);
+	init_completion(&mcast->done);
+	set_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
 	mcast->mc = ib_sa_join_multicast(&ipoib_sa_client, priv->ca,
 					 priv->port, &rec,
 					 IB_SA_MCMEMBER_REC_MGID	|
@@ -337,12 +357,14 @@ static int ipoib_mcast_sendonly_join(struct ipoib_mcast *mcast)
 	if (IS_ERR(mcast->mc)) {
 		ret = PTR_ERR(mcast->mc);
 		clear_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
-		ipoib_warn(priv, "ib_sa_join_multicast failed (ret = %d)\n",
-			   ret);
+		complete(&mcast->done);
+		ipoib_warn(priv, "ib_sa_join_multicast for sendonly join "
+			   "failed (ret = %d)\n", ret);
 	} else {
-		ipoib_dbg_mcast(priv, "no multicast record for %pI6, starting join\n",
-				mcast->mcmember.mgid.raw);
+		ipoib_dbg_mcast(priv, "no multicast record for %pI6, starting "
+				"sendonly join\n", mcast->mcmember.mgid.raw);
 	}
+	mutex_unlock(&mcast_mutex);
 
 	return ret;
 }
@@ -390,22 +412,28 @@ static int ipoib_mcast_join_complete(int status,
 	ipoib_dbg_mcast(priv, "join completion for %pI6 (status %d)\n",
 			mcast->mcmember.mgid.raw, status);
 
+	/*
+	 * We have to take the mutex to force mcast_join to
+	 * return from ib_sa_multicast_join and set mcast->mc to a
+	 * valid value.  Otherwise we were racing with ourselves in
+	 * that we might fail here, but get a valid return from
+	 * ib_sa_multicast_join after we had cleared mcast->mc here,
+	 * resulting in mis-matched joins and leaves and a deadlock
+	 */
+	mutex_lock(&mcast_mutex);
+
 	/* We trap for port events ourselves. */
-	if (status == -ENETRESET) {
-		status = 0;
+	if (status == -ENETRESET)
 		goto out;
-	}
 
 	if (!status)
 		status = ipoib_mcast_join_finish(mcast, &multicast->rec);
 
 	if (!status) {
 		mcast->backoff = 1;
-		mutex_lock(&mcast_mutex);
 		if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
 			queue_delayed_work(ipoib_workqueue,
 					   &priv->mcast_task, 0);
-		mutex_unlock(&mcast_mutex);
 
 		/*
 		 * Defer carrier on work to ipoib_workqueue to avoid a
@@ -413,37 +441,35 @@ static int ipoib_mcast_join_complete(int status,
 		 */
 		if (mcast == priv->broadcast)
 			queue_work(ipoib_workqueue, &priv->carrier_on_task);
-
-		status = 0;
-		goto out;
-	}
-
-	if (mcast->logcount++ < 20) {
-		if (status == -ETIMEDOUT || status == -EAGAIN) {
-			ipoib_dbg_mcast(priv, "multicast join failed for %pI6, status %d\n",
-					mcast->mcmember.mgid.raw, status);
-		} else {
-			ipoib_warn(priv, "multicast join failed for %pI6, status %d\n",
-				   mcast->mcmember.mgid.raw, status);
+	} else {
+		if (mcast->logcount++ < 20) {
+			if (status == -ETIMEDOUT || status == -EAGAIN) {
+				ipoib_dbg_mcast(priv, "multicast join failed for %pI6, status %d\n",
+						mcast->mcmember.mgid.raw, status);
+			} else {
+				ipoib_warn(priv, "multicast join failed for %pI6, status %d\n",
+					   mcast->mcmember.mgid.raw, status);
+			}
 		}
-	}
-
-	mcast->backoff *= 2;
-	if (mcast->backoff > IPOIB_MAX_BACKOFF_SECONDS)
-		mcast->backoff = IPOIB_MAX_BACKOFF_SECONDS;
-
-	/* Clear the busy flag so we try again */
-	status = test_and_clear_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
 
-	mutex_lock(&mcast_mutex);
+		mcast->backoff *= 2;
+		if (mcast->backoff > IPOIB_MAX_BACKOFF_SECONDS)
+			mcast->backoff = IPOIB_MAX_BACKOFF_SECONDS;
+	}
+out:
 	spin_lock_irq(&priv->lock);
-	if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
+	clear_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
+	if (status)
+		mcast->mc = NULL;
+	complete(&mcast->done);
+	if (status == -ENETRESET)
+		status = 0;
+	if (status && test_bit(IPOIB_MCAST_RUN, &priv->flags))
 		queue_delayed_work(ipoib_workqueue, &priv->mcast_task,
 				   mcast->backoff * HZ);
 	spin_unlock_irq(&priv->lock);
 	mutex_unlock(&mcast_mutex);
-out:
-	complete(&mcast->done);
+
 	return status;
 }
 
@@ -492,10 +518,9 @@ static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast,
 		rec.hop_limit	  = priv->broadcast->mcmember.hop_limit;
 	}
 
-	set_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
+	mutex_lock(&mcast_mutex);
 	init_completion(&mcast->done);
-	set_bit(IPOIB_MCAST_JOIN_STARTED, &mcast->flags);
-
+	set_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
 	mcast->mc = ib_sa_join_multicast(&ipoib_sa_client, priv->ca, priv->port,
 					 &rec, comp_mask, GFP_KERNEL,
 					 ipoib_mcast_join_complete, mcast);
@@ -509,13 +534,12 @@ static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast,
 		if (mcast->backoff > IPOIB_MAX_BACKOFF_SECONDS)
 			mcast->backoff = IPOIB_MAX_BACKOFF_SECONDS;
 
-		mutex_lock(&mcast_mutex);
 		if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
 			queue_delayed_work(ipoib_workqueue,
 					   &priv->mcast_task,
 					   mcast->backoff * HZ);
-		mutex_unlock(&mcast_mutex);
 	}
+	mutex_unlock(&mcast_mutex);
 }
 
 void ipoib_mcast_join_task(struct work_struct *work)
@@ -568,7 +592,8 @@ void ipoib_mcast_join_task(struct work_struct *work)
 	}
 
 	if (!test_bit(IPOIB_MCAST_FLAG_ATTACHED, &priv->broadcast->flags)) {
-		if (!test_bit(IPOIB_MCAST_FLAG_BUSY, &priv->broadcast->flags))
+		if (IS_ERR_OR_NULL(priv->broadcast->mc) &&
+		    !test_bit(IPOIB_MCAST_FLAG_BUSY, &priv->broadcast->flags))
 			ipoib_mcast_join(dev, priv->broadcast, 0);
 		return;
 	}
@@ -576,23 +601,33 @@ void ipoib_mcast_join_task(struct work_struct *work)
 	while (1) {
 		struct ipoib_mcast *mcast = NULL;
 
+		/*
+		 * Need the mutex so our flags are consistent, need the
+		 * priv->lock so we don't race with list removals in either
+		 * mcast_dev_flush or mcast_restart_task
+		 */
+		mutex_lock(&mcast_mutex);
 		spin_lock_irq(&priv->lock);
 		list_for_each_entry(mcast, &priv->multicast_list, list) {
-			if (!test_bit(IPOIB_MCAST_FLAG_SENDONLY, &mcast->flags)
-			    && !test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags)
-			    && !test_bit(IPOIB_MCAST_FLAG_ATTACHED, &mcast->flags)) {
+			if (IS_ERR_OR_NULL(mcast->mc) &&
+			    !test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags) &&
+			    !test_bit(IPOIB_MCAST_FLAG_ATTACHED, &mcast->flags)) {
 				/* Found the next unjoined group */
 				break;
 			}
 		}
 		spin_unlock_irq(&priv->lock);
+		mutex_unlock(&mcast_mutex);
 
 		if (&mcast->list == &priv->multicast_list) {
 			/* All done */
 			break;
 		}
 
-		ipoib_mcast_join(dev, mcast, 1);
+		if (test_bit(IPOIB_MCAST_FLAG_SENDONLY, &mcast->flags))
+			ipoib_mcast_sendonly_join(mcast);
+		else
+			ipoib_mcast_join(dev, mcast, 1);
 		return;
 	}
 
@@ -638,6 +673,9 @@ static int ipoib_mcast_leave(struct net_device *dev, struct ipoib_mcast *mcast)
 	int ret = 0;
 
 	if (test_and_clear_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags))
+		ipoib_warn(priv, "ipoib_mcast_leave on an in-flight join\n");
+
+	if (!IS_ERR_OR_NULL(mcast->mc))
 		ib_sa_free_multicast(mcast->mc);
 
 	if (test_and_clear_bit(IPOIB_MCAST_FLAG_ATTACHED, &mcast->flags)) {
@@ -690,6 +728,8 @@ void ipoib_mcast_send(struct net_device *dev, u8 *daddr, struct sk_buff *skb)
 		memcpy(mcast->mcmember.mgid.raw, mgid, sizeof (union ib_gid));
 		__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);
 	}
 
 	if (!mcast->ah) {
@@ -703,8 +743,6 @@ void ipoib_mcast_send(struct net_device *dev, u8 *daddr, struct sk_buff *skb)
 		if (test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags))
 			ipoib_dbg_mcast(priv, "no address vector, "
 					"but multicast join already started\n");
-		else if (test_bit(IPOIB_MCAST_FLAG_SENDONLY, &mcast->flags))
-			ipoib_mcast_sendonly_join(mcast);
 
 		/*
 		 * If lookup completes between here and out:, don't
@@ -766,7 +804,7 @@ void ipoib_mcast_dev_flush(struct net_device *dev)
 
 	/* seperate between the wait to the leave*/
 	list_for_each_entry_safe(mcast, tmcast, &remove_list, list)
-		if (test_bit(IPOIB_MCAST_JOIN_STARTED, &mcast->flags))
+		if (test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags))
 			wait_for_completion(&mcast->done);
 
 	list_for_each_entry_safe(mcast, tmcast, &remove_list, list) {