IB/qib: Remove atomic_inc_not_zero() from QP RCU

Follow Documentation/RCU/rcuref.txt guidance in removing
atomic_inc_not_zero() from QP RCU implementation.

This patch also removes an unneeded synchronize_rcu() in the add path.

Reviewed-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 15 insertions, 14 deletions

diff --git a/drivers/infiniband/hw/qib/qib_qp.c b/drivers/infiniband/hw/qib/qib_qp.c
index a6a2cc2ba260..c1f573a331c7 100644
--- a/drivers/infiniband/hw/qib/qib_qp.c
+++ b/drivers/infiniband/hw/qib/qib_qp.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012 Intel Corporation.  All rights reserved.
+ * Copyright (c) 2012, 2013 Intel Corporation.  All rights reserved.
  * Copyright (c) 2006 - 2012 QLogic Corporation.  * All rights reserved.
  * Copyright (c) 2005, 2006 PathScale, Inc. All rights reserved.
  *
@@ -222,8 +222,8 @@ static void insert_qp(struct qib_ibdev *dev, struct qib_qp *qp)
         unsigned long flags;
         unsigned n = qpn_hash(dev, qp->ibqp.qp_num);
 
-        spin_lock_irqsave(&dev->qpt_lock, flags);
         atomic_inc(&qp->refcount);
+        spin_lock_irqsave(&dev->qpt_lock, flags);
 
         if (qp->ibqp.qp_num == 0)
                 rcu_assign_pointer(ibp->qp0, qp);
@@ -235,7 +235,6 @@ static void insert_qp(struct qib_ibdev *dev, struct qib_qp *qp)
         }
 
         spin_unlock_irqrestore(&dev->qpt_lock, flags);
-        synchronize_rcu();
 }
 
 /*
@@ -247,36 +246,39 @@ static void remove_qp(struct qib_ibdev *dev, struct qib_qp *qp)
         struct qib_ibport *ibp = to_iport(qp->ibqp.device, qp->port_num);
         unsigned n = qpn_hash(dev, qp->ibqp.qp_num);
         unsigned long flags;
+        int removed = 1;
 
         spin_lock_irqsave(&dev->qpt_lock, flags);
 
         if (rcu_dereference_protected(ibp->qp0,
                         lockdep_is_held(&dev->qpt_lock)) == qp) {
-                atomic_dec(&qp->refcount);
                 rcu_assign_pointer(ibp->qp0, NULL);
         } else if (rcu_dereference_protected(ibp->qp1,
                         lockdep_is_held(&dev->qpt_lock)) == qp) {
-                atomic_dec(&qp->refcount);
                 rcu_assign_pointer(ibp->qp1, NULL);
         } else {
                 struct qib_qp *q;
                 struct qib_qp __rcu **qpp;
 
+                removed = 0;
                 qpp = &dev->qp_table[n];
                 for (; (q = rcu_dereference_protected(*qpp,
                                 lockdep_is_held(&dev->qpt_lock))) != NULL;
                                 qpp = &q->next)
                         if (q == qp) {
-                                atomic_dec(&qp->refcount);
                                 rcu_assign_pointer(*qpp,
                                         rcu_dereference_protected(qp->next,
                                          lockdep_is_held(&dev->qpt_lock)));
+                                removed = 1;
                                 break;
                         }
         }
 
         spin_unlock_irqrestore(&dev->qpt_lock, flags);
-        synchronize_rcu();
+        if (removed) {
+                synchronize_rcu();
+                atomic_dec(&qp->refcount);
+        }
 }
 
 /**
@@ -334,26 +336,25 @@ struct qib_qp *qib_lookup_qpn(struct qib_ibport *ibp, u32 qpn)
 {
         struct qib_qp *qp = NULL;
 
+        rcu_read_lock();
         if (unlikely(qpn <= 1)) {
-                rcu_read_lock();
                 if (qpn == 0)
                         qp = rcu_dereference(ibp->qp0);
                 else
                         qp = rcu_dereference(ibp->qp1);
+                if (qp)
+                        atomic_inc(&qp->refcount);
         } else {
                 struct qib_ibdev *dev = &ppd_from_ibp(ibp)->dd->verbs_dev;
                 unsigned n = qpn_hash(dev, qpn);
 
-                rcu_read_lock();
                 for (qp = rcu_dereference(dev->qp_table[n]); qp;
                         qp = rcu_dereference(qp->next))
-                        if (qp->ibqp.qp_num == qpn)
+                        if (qp->ibqp.qp_num == qpn) {
+                                atomic_inc(&qp->refcount);
                                 break;
+                        }
         }
-        if (qp)
-                if (unlikely(!atomic_inc_not_zero(&qp->refcount)))
-                        qp = NULL;
-
         rcu_read_unlock();
         return qp;
 }