IB/qib: Avoid returning EBUSY from MR deregister

A timing issue can occur where qib_mr_dereg can return -EBUSY if the
MR use count is not zero.

This can occur if the MR is de-registered while RDMA read response
packets are being progressed from the SDMA ring.  The suspicion is
that the peer sent an RDMA read request, which has already been copied
across to the peer.  The peer sees the completion of his request and
then communicates to the responder that the MR is not needed any
longer.  The responder tries to de-register the MR, catching some
responses remaining in the SDMA ring holding the MR use count.

The code now uses a get/put paradigm to track MR use counts and
coordinates with the MR de-registration process using a completion
when the count has reached zero.  A timeout on the delay is in place
to catch other EBUSY issues.

The reference count protocol is as follows:
- The return to the user counts as 1
- A reference from the lk_table or the qib_ibdev counts as 1.
- Transient I/O operations increase/decrease as necessary

A lot of code duplication has been folded into the new routines
init_qib_mregion() and deinit_qib_mregion().  Additionally, explicit
initialization of fields to zero is now handled by kzalloc().

Also, duplicated code 'while.*num_sge' that decrements reference
counts have been consolidated in qib_put_ss().

Reviewed-by: Ramkrishna Vepa <ramkrishna.vepa@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 10 insertions, 14 deletions

diff --git a/drivers/infiniband/hw/qib/qib_rc.c b/drivers/infiniband/hw/qib/qib_rc.c
index b641416148eb..3ab341320ead 100644
--- a/drivers/infiniband/hw/qib/qib_rc.c
+++ b/drivers/infiniband/hw/qib/qib_rc.c
@@ -95,7 +95,7 @@ static int qib_make_rc_ack(struct qib_ibdev *dev, struct qib_qp *qp,
 	case OP(RDMA_READ_RESPONSE_ONLY):
 		e = &qp->s_ack_queue[qp->s_tail_ack_queue];
 		if (e->rdma_sge.mr) {
-			atomic_dec(&e->rdma_sge.mr->refcount);
+			qib_put_mr(e->rdma_sge.mr);
 			e->rdma_sge.mr = NULL;
 		}
 		/* FALLTHROUGH */
@@ -133,7 +133,7 @@ static int qib_make_rc_ack(struct qib_ibdev *dev, struct qib_qp *qp,
 			/* Copy SGE state in case we need to resend */
 			qp->s_rdma_mr = e->rdma_sge.mr;
 			if (qp->s_rdma_mr)
-				atomic_inc(&qp->s_rdma_mr->refcount);
+				qib_get_mr(qp->s_rdma_mr);
 			qp->s_ack_rdma_sge.sge = e->rdma_sge;
 			qp->s_ack_rdma_sge.num_sge = 1;
 			qp->s_cur_sge = &qp->s_ack_rdma_sge;
@@ -172,7 +172,7 @@ static int qib_make_rc_ack(struct qib_ibdev *dev, struct qib_qp *qp,
 		qp->s_cur_sge = &qp->s_ack_rdma_sge;
 		qp->s_rdma_mr = qp->s_ack_rdma_sge.sge.mr;
 		if (qp->s_rdma_mr)
-			atomic_inc(&qp->s_rdma_mr->refcount);
+			qib_get_mr(qp->s_rdma_mr);
 		len = qp->s_ack_rdma_sge.sge.sge_length;
 		if (len > pmtu)
 			len = pmtu;
@@ -1012,7 +1012,7 @@ void qib_rc_send_complete(struct qib_qp *qp, struct qib_ib_header *hdr)
 		for (i = 0; i < wqe->wr.num_sge; i++) {
 			struct qib_sge *sge = &wqe->sg_list[i];
 
-			atomic_dec(&sge->mr->refcount);
+			qib_put_mr(sge->mr);
 		}
 		/* Post a send completion queue entry if requested. */
 		if (!(qp->s_flags & QIB_S_SIGNAL_REQ_WR) ||
@@ -1068,7 +1068,7 @@ static struct qib_swqe *do_rc_completion(struct qib_qp *qp,
 		for (i = 0; i < wqe->wr.num_sge; i++) {
 			struct qib_sge *sge = &wqe->sg_list[i];
 
-			atomic_dec(&sge->mr->refcount);
+			qib_put_mr(sge->mr);
 		}
 		/* Post a send completion queue entry if requested. */
 		if (!(qp->s_flags & QIB_S_SIGNAL_REQ_WR) ||
@@ -1730,7 +1730,7 @@ static int qib_rc_rcv_error(struct qib_other_headers *ohdr,
 		if (unlikely(offset + len != e->rdma_sge.sge_length))
 			goto unlock_done;
 		if (e->rdma_sge.mr) {
-			atomic_dec(&e->rdma_sge.mr->refcount);
+			qib_put_mr(e->rdma_sge.mr);
 			e->rdma_sge.mr = NULL;
 		}
 		if (len != 0) {
@@ -2024,11 +2024,7 @@ send_last:
 		if (unlikely(wc.byte_len > qp->r_len))
 			goto nack_inv;
 		qib_copy_sge(&qp->r_sge, data, tlen, 1);
-		while (qp->r_sge.num_sge) {
-			atomic_dec(&qp->r_sge.sge.mr->refcount);
-			if (--qp->r_sge.num_sge)
-				qp->r_sge.sge = *qp->r_sge.sg_list++;
-		}
+		qib_put_ss(&qp->r_sge);
 		qp->r_msn++;
 		if (!test_and_clear_bit(QIB_R_WRID_VALID, &qp->r_aflags))
 			break;
@@ -2116,7 +2112,7 @@ send_last:
 		}
 		e = &qp->s_ack_queue[qp->r_head_ack_queue];
 		if (e->opcode == OP(RDMA_READ_REQUEST) && e->rdma_sge.mr) {
-			atomic_dec(&e->rdma_sge.mr->refcount);
+			qib_put_mr(e->rdma_sge.mr);
 			e->rdma_sge.mr = NULL;
 		}
 		reth = &ohdr->u.rc.reth;
@@ -2188,7 +2184,7 @@ send_last:
 		}
 		e = &qp->s_ack_queue[qp->r_head_ack_queue];
 		if (e->opcode == OP(RDMA_READ_REQUEST) && e->rdma_sge.mr) {
-			atomic_dec(&e->rdma_sge.mr->refcount);
+			qib_put_mr(e->rdma_sge.mr);
 			e->rdma_sge.mr = NULL;
 		}
 		ateth = &ohdr->u.atomic_eth;
@@ -2210,7 +2206,7 @@ send_last:
 			(u64) cmpxchg((u64 *) qp->r_sge.sge.vaddr,
 				      be64_to_cpu(ateth->compare_data),
 				      sdata);
-		atomic_dec(&qp->r_sge.sge.mr->refcount);
+		qib_put_mr(qp->r_sge.sge.mr);
 		qp->r_sge.num_sge = 0;
 		e->opcode = opcode;
 		e->sent = 0;