IB/mthca: Make all device methods truly reentrant

Documentation/infiniband/core_locking.txt says:

  All of the methods in struct ib_device exported by a low-level
  driver must be fully reentrant.  The low-level driver is required to
  perform all synchronization necessary to maintain consistency, even
  if multiple function calls using the same object are run
  simultaneously.

However, mthca's modify_qp, modify_srq and resize_cq methods are
currently not reentrant.  Add a mutex to the QP, SRQ and CQ structures
so that these calls can be properly serialized.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_srq.c

diff --git a/drivers/infiniband/hw/mthca/mthca_srq.c b/drivers/infiniband/hw/mthca/mthca_srq.c
index b292fef..fab417c 100644
--- a/drivers/infiniband/hw/mthca/mthca_srq.c
+++ b/drivers/infiniband/hw/mthca/mthca_srq.c
@@ -243,6 +243,7 @@
 	spin_lock_init(&srq->lock);
 	srq->refcount = 1;
 	init_waitqueue_head(&srq->wait);
+	mutex_init(&srq->mutex);
 
 	if (mthca_is_memfree(dev))
 		mthca_arbel_init_srq_context(dev, pd, srq, mailbox->buf);
@@ -371,7 +372,11 @@
 	if (attr_mask & IB_SRQ_LIMIT) {
 		if (attr->srq_limit > srq->max)
 			return -EINVAL;
+
+		mutex_lock(&srq->mutex);
 		ret = mthca_ARM_SRQ(dev, srq->srqn, attr->srq_limit, &status);
+		mutex_unlock(&srq->mutex);
+
 		if (ret)
 			return ret;
 		if (status)