From: Eric Dumazet edumazet@google.com
[ Upstream commit 4ffdd22e49f47db543906d75453a0048a53071ab ]
As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve... 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 edumazet@google.com Cc: Zhang Yu zhangyu31@baidu.com Cc: Wang Li wangli39@baidu.com Cc: Li RongQing lirongqing@baidu.com Acked-by: Jason Wang jasowang@redhat.com Signed-off-by: Jakub Kicinski jakub.kicinski@netronome.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 aab0be40d4430..dd1d7dc361f1c 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);