[PATCH net 2/4] net/smc: fix sender_free computation

[Ursula Braun <ubraun@linux.ibm.com>]

In some scenarios a separate consumer cursor update is necessary.
The decision is made in smc_tx_consumer_cursor_update(). The
sender_free computation could be wrong:

The rx confirmed cursor is always smaller than or equal to the
rx producer cursor. The parameters in the smc_curs_diff() call
have to be exchanged, otherwise sender_free might even be negative.

And if more data arrives local_rx_ctrl.prod might be updated, enabling
a cursor difference between local_rx_ctrl.prod and rx confirmed cursor
larger than the RMB size. This case is not covered by smc_curs_diff().
Thus function smc_curs_diff_large() is introduced here.

If a recvmsg() is processed in parallel, local_tx_ctrl.cons might
change during smc_cdc_msg_send. Make sure rx_curs_confirmed is updated
with the actually sent local_tx_ctrl.cons value.

Fixes: e82f2e31f559 ("net/smc: optimize consumer cursor updates")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
---
 net/smc/smc_cdc.c |  5 +++--
 net/smc/smc_cdc.h | 26 +++++++++++++++++++++++++-
 net/smc/smc_tx.c  |  3 ++-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
index b80ef104ab4e..a712c9f8699b 100644
--- a/net/smc/smc_cdc.c
+++ b/net/smc/smc_cdc.c
@@ -91,6 +91,7 @@ int smc_cdc_msg_send(struct smc_connection *conn,
 		     struct smc_wr_buf *wr_buf,
 		     struct smc_cdc_tx_pend *pend)
 {
+	union smc_host_cursor cfed;
 	struct smc_link *link;
 	int rc;
 
@@ -102,10 +103,10 @@ int smc_cdc_msg_send(struct smc_connection *conn,
 	conn->local_tx_ctrl.seqno = conn->tx_cdc_seq;
 	smc_host_msg_to_cdc((struct smc_cdc_msg *)wr_buf,
 			    &conn->local_tx_ctrl, conn);
+	smc_curs_copy(&cfed, &((struct smc_host_cdc_msg *)wr_buf)->cons, conn);
 	rc = smc_wr_tx_send(link, (struct smc_wr_tx_pend_priv *)pend);
 	if (!rc)
-		smc_curs_copy(&conn->rx_curs_confirmed,
-			      &conn->local_tx_ctrl.cons, conn);
+		smc_curs_copy(&conn->rx_curs_confirmed, &cfed, conn);
 
 	return rc;
 }
diff --git a/net/smc/smc_cdc.h b/net/smc/smc_cdc.h
index 2148da7a26b1..271e2524dc8f 100644
--- a/net/smc/smc_cdc.h
+++ b/net/smc/smc_cdc.h
@@ -160,7 +160,9 @@ static inline void smcd_curs_copy(union smcd_cdc_cursor *tgt,
 #endif
 }
 
-/* calculate cursor difference between old and new, where old <= new */
+/* calculate cursor difference between old and new, where old <= new and
+ * difference cannot exceed size
+ */
 static inline int smc_curs_diff(unsigned int size,
 				union smc_host_cursor *old,
 				union smc_host_cursor *new)
@@ -185,6 +187,28 @@ static inline int smc_curs_comp(unsigned int size,
 	return smc_curs_diff(size, old, new);
 }
 
+/* calculate cursor difference between old and new, where old <= new and
+ * difference may exceed size
+ */
+static inline int smc_curs_diff_large(unsigned int size,
+				      union smc_host_cursor *old,
+				      union smc_host_cursor *new)
+{
+	if (old->wrap < new->wrap)
+		return min_t(int,
+			     (size - old->count) + new->count +
+			     (new->wrap - old->wrap - 1) * size,
+			     size);
+
+	if (old->wrap > new->wrap) /* wrap has switched from 0xffff to 0x0000 */
+		return min_t(int,
+			     (size - old->count) + new->count +
+			     (new->wrap + 0xffff - old->wrap) * size,
+			     size);
+
+	return max_t(int, 0, (new->count - old->count));
+}
+
 static inline void smc_host_cursor_to_cdc(union smc_cdc_cursor *peer,
 					  union smc_host_cursor *local,
 					  struct smc_connection *conn)
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 2fdfaff60cf9..f93f3580c100 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -595,7 +595,8 @@ void smc_tx_consumer_update(struct smc_connection *conn, bool force)
 	if (to_confirm > conn->rmbe_update_limit) {
 		smc_curs_copy(&prod, &conn->local_rx_ctrl.prod, conn);
 		sender_free = conn->rmb_desc->len -
-			      smc_curs_diff(conn->rmb_desc->len, &prod, &cfed);
+			      smc_curs_diff_large(conn->rmb_desc->len,
+						  &cfed, &prod);
 	}
 
 	if (conn->local_rx_ctrl.prod_flags.cons_curs_upd_req ||
-- 
2.16.4