netdev - [PATCH net-next 5/5] rds: check for excessive looping in rds_send

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Date:   Tue, 13 Aug 2019 11:21:55 -0700
From:   Gerd Rausch <gerd.rausch@...cle.com>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com
Cc:     David Miller <davem@...emloft.net>
Subject: [PATCH net-next 5/5] rds: check for excessive looping in
 rds_send_xmit

From: Andy Grover <andy.grover@...cle.com>
Date: Thu, 13 Jan 2011 11:40:31 -0800

Original commit from 2011 updated to include a change by
Yuval Shaia <yuval.shaia@...cle.com>
that adds a new statistic counter "send_stuck_rm"
to capture the messages looping exessively
in the send path.

Signed-off-by: Gerd Rausch <gerd.rausch@...cle.com>
---
 net/rds/rds.h   |  2 +-
 net/rds/send.c  | 12 ++++++++++++
 net/rds/stats.c |  1 +
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/net/rds/rds.h b/net/rds/rds.h
index f0066d168499..ad605fd61655 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -717,7 +717,7 @@ struct rds_statistics {
 	uint64_t	s_cong_send_blocked;
 	uint64_t	s_recv_bytes_added_to_socket;
 	uint64_t	s_recv_bytes_removed_from_socket;
-
+	uint64_t	s_send_stuck_rm;
 };
 
 /* af_rds.c */
diff --git a/net/rds/send.c b/net/rds/send.c
index 031b1e97a466..9ce552abf9e9 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -145,6 +145,7 @@ int rds_send_xmit(struct rds_conn_path *cp)
 	LIST_HEAD(to_be_dropped);
 	int batch_count;
 	unsigned long send_gen = 0;
+	int same_rm = 0;
 
 restart:
 	batch_count = 0;
@@ -200,6 +201,17 @@ int rds_send_xmit(struct rds_conn_path *cp)
 
 		rm = cp->cp_xmit_rm;
 
+		if (!rm) {
+			same_rm = 0;
+		} else {
+			same_rm++;
+			if (same_rm >= 4096) {
+				rds_stats_inc(s_send_stuck_rm);
+				ret = -EAGAIN;
+				break;
+			}
+		}
+
 		/*
 		 * If between sending messages, we can send a pending congestion
 		 * map update.
diff --git a/net/rds/stats.c b/net/rds/stats.c
index 6bbab4d74c4f..9e87da43c004 100644
--- a/net/rds/stats.c
+++ b/net/rds/stats.c
@@ -78,6 +78,7 @@ static const char *const rds_stat_names[] = {
 	"cong_send_blocked",
 	"recv_bytes_added_to_sock",
 	"recv_bytes_freed_fromsock",
+	"send_stuck_rm",
 };
 
 void rds_stats_info_copy(struct rds_info_iterator *iter,
-- 
2.22.0