[PATCH AUTOSEL 5.3 50/99] tun: remove possible false sharing in tun_flow_update()
From: Sasha Levin <sashal@kernel.org>
Date: 2019-10-26 13:34:45
Also in:
lkml, stable
Subsystem:
networking drivers, the rest, tun/tap driver · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn, Jason Wang
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-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 <edumazet@google.com> Cc: Zhang Yu <redacted> Cc: Wang Li <redacted> Cc: Li RongQing <redacted> Acked-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Jakub Kicinski <redacted> 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);
--
2.20.1