net/rds: Keep track of and wait for FRWR segments in use upon shutdown

Since "rds_ib_free_frmr" and "rds_ib_free_frmr_list" simply put
the FRMR memory segments on the "drop_list" or "free_list",
and it is the job of "rds_ib_flush_mr_pool" to reap those entries
by ultimately issuing a "IB_WR_LOCAL_INV" work-request,
we need to trigger and then wait for all those memory segments
attached to a particular connection to be fully released before
we can move on to release the QP, CQ, etc.

So we make "rds_ib_conn_path_shutdown" wait for one more
atomic_t called "i_fastreg_inuse_count" that keeps track of how
many FRWR memory segments are out there marked "FRMR_IS_INUSE"
(and also wake_up rds_ib_ring_empty_wait, as they go away).

Signed-off-by: Gerd Rausch <[e-mail]>
Acked-by: Santosh Shilimkar <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/rds/ib.h

···
 
 	/* To control the number of wrs from fastreg */
 	atomic_t		i_fastreg_wrs;
+	atomic_t		i_fastreg_inuse_count;
 
 	/* interrupt handling */
 	struct tasklet_struct	i_send_tasklet;

net/rds/ib_cm.c

···
 #include "rds_single_path.h"
 #include "rds.h"
 #include "ib.h"
+#include "ib_mr.h"
 
 /*
  * Set the selected protocol version
···
 				ic->i_cm_id, err);
 		}
 
+		/* kick off "flush_worker" for all pools in order to reap
+		 * all FRMR registrations that are still marked "FRMR_IS_INUSE"
+		 */
+		rds_ib_flush_mrs();
+
 		/*
 		 * We want to wait for tx and rx completion to finish
 		 * before we tear down the connection, but we have to be
···
 		wait_event(rds_ib_ring_empty_wait,
 			   rds_ib_ring_empty(&ic->i_recv_ring) &&
 			   (atomic_read(&ic->i_signaled_sends) == 0) &&
+			   (atomic_read(&ic->i_fastreg_inuse_count) == 0) &&
 			   (atomic_read(&ic->i_fastreg_wrs) == RDS_IB_DEFAULT_FR_WR));
 		tasklet_kill(&ic->i_send_tasklet);
 		tasklet_kill(&ic->i_recv_tasklet);

net/rds/ib_frmr.c

···
 
 #include "ib_mr.h"
 
+static inline void
+rds_transition_frwr_state(struct rds_ib_mr *ibmr,
+			  enum rds_ib_fr_state old_state,
+			  enum rds_ib_fr_state new_state)
+{
+	if (cmpxchg(&ibmr->u.frmr.fr_state,
+		    old_state, new_state) == old_state &&
+	    old_state == FRMR_IS_INUSE) {
+		/* enforce order of ibmr->u.frmr.fr_state update
+		 * before decrementing i_fastreg_inuse_count
+		 */
+		smp_mb__before_atomic();
+		atomic_dec(&ibmr->ic->i_fastreg_inuse_count);
+		if (waitqueue_active(&rds_ib_ring_empty_wait))
+			wake_up(&rds_ib_ring_empty_wait);
+	}
+}
+
 static struct rds_ib_mr *rds_ib_alloc_frmr(struct rds_ib_device *rds_ibdev,
 					   int npages)
 {
···
 	if (unlikely(ret != ibmr->sg_len))
 		return ret < 0 ? ret : -EINVAL;
 
+	if (cmpxchg(&frmr->fr_state,
+		    FRMR_IS_FREE, FRMR_IS_INUSE) != FRMR_IS_FREE)
+		return -EBUSY;
+
+	atomic_inc(&ibmr->ic->i_fastreg_inuse_count);
+
 	/* Perform a WR for the fast_reg_mr. Each individual page
 	 * in the sg list is added to the fast reg page list and placed
 	 * inside the fast_reg_mr WR.  The key used is a rolling 8bit
 	 * counter, which should guarantee uniqueness.
 	 */
 	ib_update_fast_reg_key(frmr->mr, ibmr->remap_count++);
-	frmr->fr_state = FRMR_IS_INUSE;
 	frmr->fr_reg = true;
 
 	memset(&reg_wr, 0, sizeof(reg_wr));
···
 	ret = ib_post_send(ibmr->ic->i_cm_id->qp, &reg_wr.wr, NULL);
 	if (unlikely(ret)) {
 		/* Failure here can be because of -ENOMEM as well */
-		frmr->fr_state = FRMR_IS_STALE;
+		rds_transition_frwr_state(ibmr, FRMR_IS_INUSE, FRMR_IS_STALE);
+
 		atomic_inc(&ibmr->ic->i_fastreg_wrs);
 		if (printk_ratelimit())
 			pr_warn("RDS/IB: %s returned error(%d)\n",
···
 
 	ret = ib_post_send(i_cm_id->qp, s_wr, NULL);
 	if (unlikely(ret)) {
-		frmr->fr_state = FRMR_IS_STALE;
+		rds_transition_frwr_state(ibmr, FRMR_IS_INUSE, FRMR_IS_STALE);
 		frmr->fr_inv = false;
+		/* enforce order of frmr->fr_inv update
+		 * before incrementing i_fastreg_wrs
+		 */
+		smp_mb__before_atomic();
 		atomic_inc(&ibmr->ic->i_fastreg_wrs);
 		pr_err("RDS/IB: %s returned error(%d)\n", __func__, ret);
 		goto out;
···
 	struct rds_ib_frmr *frmr = &ibmr->u.frmr;
 
 	if (wc->status != IB_WC_SUCCESS) {
-		frmr->fr_state = FRMR_IS_STALE;
+		rds_transition_frwr_state(ibmr, FRMR_IS_INUSE, FRMR_IS_STALE);
 		if (rds_conn_up(ic->conn))
 			rds_ib_conn_error(ic->conn,
 					  "frmr completion <%pI4,%pI4> status %u(%s), vendor_err 0x%x, disconnecting and reconnecting\n",
···
 	}
 
 	if (frmr->fr_inv) {
-		if (frmr->fr_state == FRMR_IS_INUSE)
-			frmr->fr_state = FRMR_IS_FREE;
+		rds_transition_frwr_state(ibmr, FRMR_IS_INUSE, FRMR_IS_FREE);
 		frmr->fr_inv = false;
 		wake_up(&frmr->fr_inv_done);
 	}
···
 		wake_up(&frmr->fr_reg_done);
 	}
 
+	/* enforce order of frmr->{fr_reg,fr_inv} update
+	 * before incrementing i_fastreg_wrs
+	 */
+	smp_mb__before_atomic();
 	atomic_inc(&ic->i_fastreg_wrs);
 }