IPoIB: Use a private hash table for path lookup in xmit path

Dave Miller <davem@davemloft.net> provided a detailed description of
why the way IPoIB is using neighbours for its own ipoib_neigh struct
is buggy:

    Any time an ipoib_neigh is changed, a sequence like the following is made:

    			spin_lock_irqsave(&priv->lock, flags);
    			/*
    			 * It's safe to call ipoib_put_ah() inside
    			 * priv->lock here, because we know that
    			 * path->ah will always hold one more reference,
    			 * so ipoib_put_ah() will never do more than
    			 * decrement the ref count.
    			 */
    			if (neigh->ah)
    				ipoib_put_ah(neigh->ah);
    			list_del(&neigh->list);
    			ipoib_neigh_free(dev, neigh);
    			spin_unlock_irqrestore(&priv->lock, flags);
    			ipoib_path_lookup(skb, n, dev);

    This doesn't work, because you're leaving a stale pointer to the freed up
    ipoib_neigh in the special neigh->ha pointer cookie.  Yes, it even fails
    with all the locking done to protect _changes_ to *ipoib_neigh(n), and
    with the code in ipoib_neigh_free() that NULLs out the pointer.

    The core issue is that read side calls to *to_ipoib_neigh(n) are not
    being synchronized at all, they are performed without any locking.  So
    whether we hold the lock or not when making changes to *ipoib_neigh(n)
    you still can have threads see references to freed up ipoib_neigh
    objects.

    	cpu 1			cpu 2
    	n = *ipoib_neigh()
    				*ipoib_neigh() = NULL
    				kfree(n)
    	n->foo == OOPS

    [..]

    Perhaps the ipoib code can have a private path database it manages
    entirely itself, which holds all the necessary information and is
    looked up by some generic key which is available easily at transmit
    time and does not involve generic neighbour entries.

See <http://marc.info/?l=linux-rdma&m=132812793105624&w=2> and
<http://marc.info/?l=linux-rdma&w=2&r=1&s=allows+references+to+freed+memory&q=b>
for the full discussion.

This patch aims to solve the race conditions found in the IPoIB driver.

The patch removes the connection between the core networking neighbour
structure and the ipoib_neigh structure.  In addition to avoiding the
race described above, it allows us to handle SKBs carrying IP packets
that don't have any associated neighbour.

We add an ipoib_neigh hash table with N buckets where the key is the
destination hardware address.  The ipoib_neigh is fetched from the
hash table and instead of the stashed location in the neighbour
structure. The hash table uses both RCU and reference counting to
guarantee that no ipoib_neigh instance is ever deleted while in use.

Fetching the ipoib_neigh structure instance from the hash also makes
the special code in ipoib_start_xmit that handles remote and local
bonding failover redundant.

Aged ipoib_neigh instances are deleted by a garbage collection task
that runs every M seconds and deletes every ipoib_neigh instance that
was idle for at least 2*M seconds. The deletion is safe since the
ipoib_neigh instances are protected using RCU and reference count
mechanisms.

The number of buckets (N) and frequency of running the GC thread (M),
are taken from the exported arb_tbl.

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

1 files changed, 36 insertions, 20 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h
index 86df632ea612..ca43901ed861 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib.h
+++ b/drivers/infiniband/ulp/ipoib/ipoib.h
@@ -92,6 +92,8 @@ enum {
 	IPOIB_STOP_REAPER	  = 7,
 	IPOIB_FLAG_ADMIN_CM	  = 9,
 	IPOIB_FLAG_UMCAST	  = 10,
+	IPOIB_STOP_NEIGH_GC	  = 11,
+	IPOIB_NEIGH_TBL_FLUSH	  = 12,
 
 	IPOIB_MAX_BACKOFF_SECONDS = 16,
 
@@ -260,6 +262,20 @@ struct ipoib_ethtool_st {
 	u16     max_coalesced_frames;
 };
 
+struct ipoib_neigh_hash {
+	struct ipoib_neigh __rcu      **buckets;
+	struct rcu_head			rcu;
+	u32				mask;
+	u32				size;
+};
+
+struct ipoib_neigh_table {
+	struct ipoib_neigh_hash __rcu  *htbl;
+	rwlock_t			rwlock;
+	atomic_t			entries;
+	struct completion		flushed;
+};
+
 /*
  * Device private locking: network stack tx_lock protects members used
  * in TX fast path, lock protects everything else.  lock nests inside
@@ -279,6 +295,8 @@ struct ipoib_dev_priv {
 	struct rb_root  path_tree;
 	struct list_head path_list;
 
+	struct ipoib_neigh_table ntbl;
+
 	struct ipoib_mcast *broadcast;
 	struct list_head multicast_list;
 	struct rb_root multicast_tree;
@@ -291,7 +309,7 @@ struct ipoib_dev_priv {
 	struct work_struct flush_heavy;
 	struct work_struct restart_task;
 	struct delayed_work ah_reap_task;
-
+	struct delayed_work neigh_reap_task;
 	struct ib_device *ca;
 	u8		  port;
 	u16		  pkey;
@@ -377,13 +395,16 @@ struct ipoib_neigh {
 #ifdef CONFIG_INFINIBAND_IPOIB_CM
 	struct ipoib_cm_tx *cm;
 #endif
-	union ib_gid	    dgid;
+	u8     daddr[INFINIBAND_ALEN];
 	struct sk_buff_head queue;
 
-	struct neighbour   *neighbour;
 	struct net_device *dev;
 
 	struct list_head    list;
+	struct ipoib_neigh __rcu *hnext;
+	struct rcu_head     rcu;
+	atomic_t	    refcnt;
+	unsigned long       alive;
 };
 
 #define IPOIB_UD_MTU(ib_mtu)		(ib_mtu - IPOIB_ENCAP_LEN)
@@ -394,21 +415,17 @@ static inline int ipoib_ud_need_sg(unsigned int ib_mtu)
 	return IPOIB_UD_BUF_SIZE(ib_mtu) > PAGE_SIZE;
 }
 
-/*
- * We stash a pointer to our private neighbour information after our
- * hardware address in neigh->ha.  The ALIGN() expression here makes
- * sure that this pointer is stored aligned so that an unaligned
- * load is not needed to dereference it.
- */
-static inline struct ipoib_neigh **to_ipoib_neigh(struct neighbour *neigh)
+void ipoib_neigh_dtor(struct ipoib_neigh *neigh);
+static inline void ipoib_neigh_put(struct ipoib_neigh *neigh)
 {
-	return (void*) neigh + ALIGN(offsetof(struct neighbour, ha) +
-				     INFINIBAND_ALEN, sizeof(void *));
+	if (atomic_dec_and_test(&neigh->refcnt))
+		ipoib_neigh_dtor(neigh);
 }
-
-struct ipoib_neigh *ipoib_neigh_alloc(struct neighbour *neigh,
+struct ipoib_neigh *ipoib_neigh_get(struct net_device *dev, u8 *daddr);
+struct ipoib_neigh *ipoib_neigh_alloc(u8 *daddr,
 				      struct net_device *dev);
-void ipoib_neigh_free(struct net_device *dev, struct ipoib_neigh *neigh);
+void ipoib_neigh_free(struct ipoib_neigh *neigh);
+void ipoib_del_neighs_by_gid(struct net_device *dev, u8 *gid);
 
 extern struct workqueue_struct *ipoib_workqueue;
 
@@ -425,7 +442,6 @@ static inline void ipoib_put_ah(struct ipoib_ah *ah)
 {
 	kref_put(&ah->ref, ipoib_free_ah);
 }
-
 int ipoib_open(struct net_device *dev);
 int ipoib_add_pkey_attr(struct net_device *dev);
 int ipoib_add_umcast_attr(struct net_device *dev);
@@ -455,7 +471,7 @@ void ipoib_dev_cleanup(struct net_device *dev);
 
 void ipoib_mcast_join_task(struct work_struct *work);
 void ipoib_mcast_carrier_on_task(struct work_struct *work);
-void ipoib_mcast_send(struct net_device *dev, void *mgid, struct sk_buff *skb);
+void ipoib_mcast_send(struct net_device *dev, u8 *daddr, struct sk_buff *skb);
 
 void ipoib_mcast_restart_task(struct work_struct *work);
 int ipoib_mcast_start_thread(struct net_device *dev);
@@ -517,10 +533,10 @@ static inline int ipoib_cm_admin_enabled(struct net_device *dev)
 		test_bit(IPOIB_FLAG_ADMIN_CM, &priv->flags);
 }
 
-static inline int ipoib_cm_enabled(struct net_device *dev, struct neighbour *n)
+static inline int ipoib_cm_enabled(struct net_device *dev, u8 *hwaddr)
 {
 	struct ipoib_dev_priv *priv = netdev_priv(dev);
-	return IPOIB_CM_SUPPORTED(n->ha) &&
+	return IPOIB_CM_SUPPORTED(hwaddr) &&
 		test_bit(IPOIB_FLAG_ADMIN_CM, &priv->flags);
 }
 
@@ -575,7 +591,7 @@ static inline int ipoib_cm_admin_enabled(struct net_device *dev)
 {
 	return 0;
 }
-static inline int ipoib_cm_enabled(struct net_device *dev, struct neighbour *n)
+static inline int ipoib_cm_enabled(struct net_device *dev, u8 *hwaddr)
 
 {
 	return 0;