RDS/IB: add refcount tracking to struct rds_ib_device

The RDS IB client .remove callback used to free the rds_ibdev for the given
device unconditionally.  This could race other users of the struct.  This patch
adds refcounting so that we only free the rds_ibdev once all of its users are
done.

Many rds_ibdev users are tied to connections.  We give the connection a
reference and change these users to reference the device in the connection
instead of looking it up in the IB client data.  The only user of the IB client
data remaining is the first lookup of the device as connections are built up.

Incrementing the reference count of a device found in the IB client data could
race with final freeing so we use an RCU grace period to make sure that freeing
won't happen until those lookups are done.

MRs need the rds_ibdev to get at the pool that they're freed in to.  They exist
outside a connection and many MRs can reference different devices from one
socket, so it was natural to have each MR hold a reference.  MR refs can be
dropped from interrupt handlers and final device teardown can block so we push
it off to a work struct.  Pool teardown had to be fixed to cancel its pending
work instead of deadlocking waiting for all queued work, including itself, to
finish.

MRs get their reference from the global device list, which gets a reference.
It is left unprotected by locks and remains racy.  A simple global lock would
be a significant bottleneck.  More scalable (complicated) locking should be
done carefully in a later patch.

Signed-off-by: Zach Brown <zach.brown@oracle.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/net/rds/ib_rdma.c b/net/rds/ib_rdma.c
index 4ba01b9..64b5ede 100644
--- a/net/rds/ib_rdma.c
+++ b/net/rds/ib_rdma.c
@@ -87,6 +87,7 @@ static struct rds_ib_device *rds_ib_get_device(__be32 ipaddr)
 		rcu_read_lock();
 		list_for_each_entry_rcu(i_ipaddr, &rds_ibdev->ipaddr_list, list) {
 			if (i_ipaddr->ipaddr == ipaddr) {
+				atomic_inc(&rds_ibdev->refcount);
 				rcu_read_unlock();
 				return rds_ibdev;
 			}
@@ -141,8 +142,10 @@ int rds_ib_update_ipaddr(struct rds_ib_device *rds_ibdev, __be32 ipaddr)
 	struct rds_ib_device *rds_ibdev_old;
 
 	rds_ibdev_old = rds_ib_get_device(ipaddr);
-	if (rds_ibdev_old)
+	if (rds_ibdev_old) {
 		rds_ib_remove_ipaddr(rds_ibdev_old, ipaddr);
+		rds_ib_dev_put(rds_ibdev_old);
+	}
 
 	return rds_ib_add_ipaddr(rds_ibdev, ipaddr);
 }
@@ -163,6 +166,7 @@ void rds_ib_add_conn(struct rds_ib_device *rds_ibdev, struct rds_connection *con
 	spin_unlock_irq(&ib_nodev_conns_lock);
 
 	ic->rds_ibdev = rds_ibdev;
+	atomic_inc(&rds_ibdev->refcount);
 }
 
 void rds_ib_remove_conn(struct rds_ib_device *rds_ibdev, struct rds_connection *conn)
@@ -182,6 +186,7 @@ void rds_ib_remove_conn(struct rds_ib_device *rds_ibdev, struct rds_connection *
 	spin_unlock(&ib_nodev_conns_lock);
 
 	ic->rds_ibdev = NULL;
+	rds_ib_dev_put(rds_ibdev);
 }
 
 void __rds_ib_destroy_conns(struct list_head *list, spinlock_t *list_lock)
@@ -240,7 +245,7 @@ void rds_ib_get_mr_info(struct rds_ib_device *rds_ibdev, struct rds_info_rdma_co
 
 void rds_ib_destroy_mr_pool(struct rds_ib_mr_pool *pool)
 {
-	flush_workqueue(rds_wq);
+	cancel_work_sync(&pool->flush_worker);
 	rds_ib_flush_mr_pool(pool, 1);
 	WARN_ON(atomic_read(&pool->item_count));
 	WARN_ON(atomic_read(&pool->free_pinned));
@@ -597,6 +602,8 @@ void rds_ib_free_mr(void *trans_private, int invalidate)
 			queue_work(rds_wq, &pool->flush_worker);
 		}
 	}
+
+	rds_ib_dev_put(rds_ibdev);
 }
 
 void rds_ib_flush_mrs(void)
@@ -640,6 +647,7 @@ void *rds_ib_get_mr(struct scatterlist *sg, unsigned long nents,
 		printk(KERN_WARNING "RDS/IB: map_fmr failed (errno=%d)\n", ret);
 
 	ibmr->device = rds_ibdev;
+	rds_ibdev = NULL;
 
  out:
 	if (ret) {
@@ -647,5 +655,7 @@ void *rds_ib_get_mr(struct scatterlist *sg, unsigned long nents,
 			rds_ib_free_mr(ibmr, 0);
 		ibmr = ERR_PTR(ret);
 	}
+	if (rds_ibdev)
+		rds_ib_dev_put(rds_ibdev);
 	return ibmr;
 }