On 2019/10/10 上午12:20, Eric Dumazet wrote:
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 <eduma...@google.com> Cc: Zhang Yu <zhangy...@baidu.com> Cc: Wang Li <wangl...@baidu.com> Cc: Li RongQing <lirongq...@baidu.com> Cc: Jason Wang <jasow...@redhat.com> --- 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);
Acked-by: Jason Wang <jasow...@redhat.com>
