From 4ffdd22e49f47db543906d75453a0048a53071ab Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 9 Oct 2019 09:20:02 -0700 Subject: tun: remove possible false sharing in tun_flow_update() 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 Cc: Zhang Yu Cc: Wang Li Cc: Li RongQing Acked-by: Jason Wang Signed-off-by: Jakub Kicinski --- drivers/net/tun.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/net/tun.c') diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 812dc3a65efb..a8d3141582a5 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); -- cgit