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Subject[PATCH net] rds: Fix incorrect statistics counting
Date
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 <haakon.bugge@oracle.com>
Reviewed-by: Knut Omang <knut.omang@oracle.com>
---
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
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