As mentioned in
https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
a C compiler can legally transform
if (e->queue_index != queue_index)
e->queue_index = queue_index;
to :
e->queue_index = queue_index;
Note that the code using jiffies has no issue, since jiffies
has volatile attribute.
if (e->updated != jiffies)
e->updated = jiffies;
Fixes: 83b1bc122cab ("tun: align write-heavy flow entry members to a cache
line")
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Zhang Yu <[email protected]>
Cc: Wang Li <[email protected]>
Cc: Li RongQing <[email protected]>
Cc: Jason Wang <[email protected]>
---
drivers/net/tun.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index
812dc3a65efbb9d1ee2724e73978dbc4803ec171..a8d3141582a53caf407dc9aff61c452998de068f
100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -526,8 +526,8 @@ static void tun_flow_update(struct tun_struct *tun, u32
rxhash,
e = tun_flow_find(head, rxhash);
if (likely(e)) {
/* TODO: keep queueing to old queue until it's empty? */
- if (e->queue_index != queue_index)
- e->queue_index = queue_index;
+ if (READ_ONCE(e->queue_index) != queue_index)
+ WRITE_ONCE(e->queue_index, queue_index);
if (e->updated != jiffies)
e->updated = jiffies;
sock_rps_record_flow_hash(e->rps_rxhash);
--
2.23.0.581.g78d2f28ef7-goog
