[PATCH net] rds: Fix incorrect statistics counting
From: Håkon Bugge <hidden>
Date: 2017-09-06 15:30:55
Also in:
linux-rdma, lkml
Subsystem:
networking [general], rds - reliable datagram sockets, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Allison Henderson, Linus Torvalds
In rds_send_xmit() there is logic to batch the sends. However, if another thread has acquired the lock, it is considered a race and we yield. The code incrementing the s_send_lock_queue_raced statistics counter did not count this event correctly. This commit removes a small race in determining the race and increments the statistics counter correctly. Signed-off-by: Håkon Bugge <redacted> Reviewed-by: Knut Omang <redacted> --- net/rds/send.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/net/rds/send.c b/net/rds/send.c
index 058a407..ecfe0b5 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c@@ -101,6 +101,11 @@ void rds_send_path_reset(struct rds_conn_path *cp) } EXPORT_SYMBOL_GPL(rds_send_path_reset); +static bool someone_in_xmit(struct rds_conn_path *cp) +{ + return test_bit(RDS_IN_XMIT, &cp->cp_flags); +} + static int acquire_in_xmit(struct rds_conn_path *cp) { return test_and_set_bit(RDS_IN_XMIT, &cp->cp_flags) == 0;
@@ -428,14 +433,19 @@ int rds_send_xmit(struct rds_conn_path *cp) * some work and we will skip our goto */ if (ret == 0) { + bool raced; + smp_mb(); + raced = someone_in_xmit(cp) || + send_gen != READ_ONCE(cp->cp_send_gen); + if ((test_bit(0, &conn->c_map_queued) || - !list_empty(&cp->cp_send_queue)) && - send_gen == READ_ONCE(cp->cp_send_gen)) { - rds_stats_inc(s_send_lock_queue_raced); + !list_empty(&cp->cp_send_queue)) && !raced) { if (batch_count < send_batch_count) goto restart; queue_delayed_work(rds_wq, &cp->cp_send_w, 1); + } else if (raced) { + rds_stats_inc(s_send_lock_queue_raced); } } out:
--
2.9.3