IPoIB: Fix AB-BA deadlock when deleting neighbours

Lockdep points out a circular locking dependency betwwen the ipoib
device priv spinlock (priv->lock) and the neighbour table rwlock
(ntbl->rwlock).

In the normal path, ie neigbour garbage collection task, the neigh
table rwlock is taken first and then if the neighbour needs to be
deleted, priv->lock is taken.

However in some error paths, such as in ipoib_cm_handle_tx_wc(),
priv->lock is taken first and then ipoib_neigh_free routine is called
which in turn takes the neighbour table ntbl->rwlock.

The solution is to get rid the neigh table rwlock completely and use
only priv->lock.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

3 files changed, 27 insertions, 46 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h
index e6bbeae1c30..0af216d21f8 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib.h
+++ b/drivers/infiniband/ulp/ipoib/ipoib.h
@@ -274,7 +274,6 @@ struct ipoib_neigh_hash {
 
 struct ipoib_neigh_table {
         struct ipoib_neigh_hash __rcu  *htbl;
-        rwlock_t                        rwlock;
         atomic_t                        entries;
         struct completion               flushed;
         struct completion               deleted;
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index 72c1fc28f07..1e19b5ae7c4 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -546,15 +546,15 @@ static void neigh_add_path(struct sk_buff *skb, u8 *daddr,
         struct ipoib_neigh *neigh;
         unsigned long flags;
 
+        spin_lock_irqsave(&priv->lock, flags);
         neigh = ipoib_neigh_alloc(daddr, dev);
         if (!neigh) {
+                spin_unlock_irqrestore(&priv->lock, flags);
                 ++dev->stats.tx_dropped;
                 dev_kfree_skb_any(skb);
                 return;
         }
 
-        spin_lock_irqsave(&priv->lock, flags);
-
         path = __path_find(dev, daddr + 4);
         if (!path) {
                 path = path_rec_create(dev, daddr + 4);
@@ -863,10 +863,10 @@ static void __ipoib_reap_neigh(struct ipoib_dev_priv *priv)
         if (test_bit(IPOIB_STOP_NEIGH_GC, &priv->flags))
                 return;
 
-        write_lock_bh(&ntbl->rwlock);
+        spin_lock_irqsave(&priv->lock, flags);
 
         htbl = rcu_dereference_protected(ntbl->htbl,
-                                         lockdep_is_held(&ntbl->rwlock));
+                                         lockdep_is_held(&priv->lock));
 
         if (!htbl)
                 goto out_unlock;
@@ -883,16 +883,14 @@ static void __ipoib_reap_neigh(struct ipoib_dev_priv *priv)
                 struct ipoib_neigh __rcu **np = &htbl->buckets[i];
 
                 while ((neigh = rcu_dereference_protected(*np,
-                                                          lockdep_is_held(&ntbl->rwlock))) != NULL) {
+                                                          lockdep_is_held(&priv->lock))) != NULL) {
                         /* was the neigh idle for two GC periods */
                         if (time_after(neigh_obsolete, neigh->alive)) {
                                 rcu_assign_pointer(*np,
                                                    rcu_dereference_protected(neigh->hnext,
-                                                                             lockdep_is_held(&ntbl->rwlock)));
+                                                                             lockdep_is_held(&priv->lock)));
                                 /* remove from path/mc list */
-                                spin_lock_irqsave(&priv->lock, flags);
                                 list_del(&neigh->list);
-                                spin_unlock_irqrestore(&priv->lock, flags);
                                 call_rcu(&neigh->rcu, ipoib_neigh_reclaim);
                         } else {
                                 np = &neigh->hnext;
@@ -902,7 +900,7 @@ static void __ipoib_reap_neigh(struct ipoib_dev_priv *priv)
         }
 
 out_unlock:
-        write_unlock_bh(&ntbl->rwlock);
+        spin_unlock_irqrestore(&priv->lock, flags);
 }
 
 static void ipoib_reap_neigh(struct work_struct *work)
@@ -947,10 +945,8 @@ struct ipoib_neigh *ipoib_neigh_alloc(u8 *daddr,
         struct ipoib_neigh *neigh;
         u32 hash_val;
 
-        write_lock_bh(&ntbl->rwlock);
-
         htbl = rcu_dereference_protected(ntbl->htbl,
-                                         lockdep_is_held(&ntbl->rwlock));
+                                         lockdep_is_held(&priv->lock));
         if (!htbl) {
                 neigh = NULL;
                 goto out_unlock;
@@ -961,10 +957,10 @@ struct ipoib_neigh *ipoib_neigh_alloc(u8 *daddr,
          */
         hash_val = ipoib_addr_hash(htbl, daddr);
         for (neigh = rcu_dereference_protected(htbl->buckets[hash_val],
-                                               lockdep_is_held(&ntbl->rwlock));
+                                               lockdep_is_held(&priv->lock));
              neigh != NULL;
              neigh = rcu_dereference_protected(neigh->hnext,
-                                               lockdep_is_held(&ntbl->rwlock))) {
+                                               lockdep_is_held(&priv->lock))) {
                 if (memcmp(daddr, neigh->daddr, INFINIBAND_ALEN) == 0) {
                         /* found, take one ref on behalf of the caller */
                         if (!atomic_inc_not_zero(&neigh->refcnt)) {
@@ -987,12 +983,11 @@ struct ipoib_neigh *ipoib_neigh_alloc(u8 *daddr,
         /* put in hash */
         rcu_assign_pointer(neigh->hnext,
                            rcu_dereference_protected(htbl->buckets[hash_val],
-                                                     lockdep_is_held(&ntbl->rwlock)));
+                                                     lockdep_is_held(&priv->lock)));
         rcu_assign_pointer(htbl->buckets[hash_val], neigh);
         atomic_inc(&ntbl->entries);
 
 out_unlock:
-        write_unlock_bh(&ntbl->rwlock);
 
         return neigh;
 }
@@ -1040,35 +1035,29 @@ void ipoib_neigh_free(struct ipoib_neigh *neigh)
         struct ipoib_neigh *n;
         u32 hash_val;
 
-        write_lock_bh(&ntbl->rwlock);
-
         htbl = rcu_dereference_protected(ntbl->htbl,
-                                        lockdep_is_held(&ntbl->rwlock));
+                                        lockdep_is_held(&priv->lock));
         if (!htbl)
-                goto out_unlock;
+                return;
 
         hash_val = ipoib_addr_hash(htbl, neigh->daddr);
         np = &htbl->buckets[hash_val];
         for (n = rcu_dereference_protected(*np,
-                                            lockdep_is_held(&ntbl->rwlock));
+                                            lockdep_is_held(&priv->lock));
              n != NULL;
              n = rcu_dereference_protected(*np,
-                                        lockdep_is_held(&ntbl->rwlock))) {
+                                        lockdep_is_held(&priv->lock))) {
                 if (n == neigh) {
                         /* found */
                         rcu_assign_pointer(*np,
                                            rcu_dereference_protected(neigh->hnext,
-                                                                     lockdep_is_held(&ntbl->rwlock)));
+                                                                     lockdep_is_held(&priv->lock)));
                         call_rcu(&neigh->rcu, ipoib_neigh_reclaim);
-                        goto out_unlock;
+                        return;
                 } else {
                         np = &n->hnext;
                 }
         }
-
-out_unlock:
-        write_unlock_bh(&ntbl->rwlock);
-
 }
 
 static int ipoib_neigh_hash_init(struct ipoib_dev_priv *priv)
@@ -1080,7 +1069,6 @@ static int ipoib_neigh_hash_init(struct ipoib_dev_priv *priv)
 
         clear_bit(IPOIB_NEIGH_TBL_FLUSH, &priv->flags);
         ntbl->htbl = NULL;
-        rwlock_init(&ntbl->rwlock);
         htbl = kzalloc(sizeof(*htbl), GFP_KERNEL);
         if (!htbl)
                 return -ENOMEM;
@@ -1128,10 +1116,10 @@ void ipoib_del_neighs_by_gid(struct net_device *dev, u8 *gid)
         int i;
 
         /* remove all neigh connected to a given path or mcast */
-        write_lock_bh(&ntbl->rwlock);
+        spin_lock_irqsave(&priv->lock, flags);
 
         htbl = rcu_dereference_protected(ntbl->htbl,
-                                         lockdep_is_held(&ntbl->rwlock));
+                                         lockdep_is_held(&priv->lock));
 
         if (!htbl)
                 goto out_unlock;
@@ -1141,16 +1129,14 @@ void ipoib_del_neighs_by_gid(struct net_device *dev, u8 *gid)
                 struct ipoib_neigh __rcu **np = &htbl->buckets[i];
 
                 while ((neigh = rcu_dereference_protected(*np,
-                                                          lockdep_is_held(&ntbl->rwlock))) != NULL) {
+                                                          lockdep_is_held(&priv->lock))) != NULL) {
                         /* delete neighs belong to this parent */
                         if (!memcmp(gid, neigh->daddr + 4, sizeof (union ib_gid))) {
                                 rcu_assign_pointer(*np,
                                                    rcu_dereference_protected(neigh->hnext,
-                                                                             lockdep_is_held(&ntbl->rwlock)));
+                                                                             lockdep_is_held(&priv->lock)));
                                 /* remove from parent list */
-                                spin_lock_irqsave(&priv->lock, flags);
                                 list_del(&neigh->list);
-                                spin_unlock_irqrestore(&priv->lock, flags);
                                 call_rcu(&neigh->rcu, ipoib_neigh_reclaim);
                         } else {
                                 np = &neigh->hnext;
@@ -1159,7 +1145,7 @@ void ipoib_del_neighs_by_gid(struct net_device *dev, u8 *gid)
                 }
         }
 out_unlock:
-        write_unlock_bh(&ntbl->rwlock);
+        spin_unlock_irqrestore(&priv->lock, flags);
 }
 
 static void ipoib_flush_neighs(struct ipoib_dev_priv *priv)
@@ -1171,10 +1157,10 @@ static void ipoib_flush_neighs(struct ipoib_dev_priv *priv)
 
         init_completion(&priv->ntbl.flushed);
 
-        write_lock_bh(&ntbl->rwlock);
+        spin_lock_irqsave(&priv->lock, flags);
 
         htbl = rcu_dereference_protected(ntbl->htbl,
-                                        lockdep_is_held(&ntbl->rwlock));
+                                        lockdep_is_held(&priv->lock));
         if (!htbl)
                 goto out_unlock;
 
@@ -1187,14 +1173,12 @@ static void ipoib_flush_neighs(struct ipoib_dev_priv *priv)
                 struct ipoib_neigh __rcu **np = &htbl->buckets[i];
 
                 while ((neigh = rcu_dereference_protected(*np,
-                                                          lockdep_is_held(&ntbl->rwlock))) != NULL) {
+                                       lockdep_is_held(&priv->lock))) != NULL) {
                         rcu_assign_pointer(*np,
                                            rcu_dereference_protected(neigh->hnext,
-                                                                     lockdep_is_held(&ntbl->rwlock)));
+                                                                     lockdep_is_held(&priv->lock)));
                         /* remove from path/mc list */
-                        spin_lock_irqsave(&priv->lock, flags);
                         list_del(&neigh->list);
-                        spin_unlock_irqrestore(&priv->lock, flags);
                         call_rcu(&neigh->rcu, ipoib_neigh_reclaim);
                 }
         }
@@ -1204,7 +1188,7 @@ free_htbl:
         call_rcu(&htbl->rcu, neigh_hash_free_rcu);
 
 out_unlock:
-        write_unlock_bh(&ntbl->rwlock);
+        spin_unlock_irqrestore(&priv->lock, flags);
         if (wait_flushed)
                 wait_for_completion(&priv->ntbl.flushed);
 }
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
index 13f4aa7593c..75367249f44 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
@@ -707,9 +707,7 @@ out:
                 neigh = ipoib_neigh_get(dev, daddr);
                 spin_lock_irqsave(&priv->lock, flags);
                 if (!neigh) {
-                        spin_unlock_irqrestore(&priv->lock, flags);
                         neigh = ipoib_neigh_alloc(daddr, dev);
-                        spin_lock_irqsave(&priv->lock, flags);
                         if (neigh) {
                                 kref_get(&mcast->ah->ref);
                                 neigh->ah       = mcast->ah;