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Date: Tue, 7 May 2019 00:03:36 -0400 From: Jason Wang <jasowang@...hat.com> To: netdev@...r.kernel.org Cc: mst@...hat.com, Jason Wang <jasowang@...hat.com>, YueHaibing <yuehaibing@...wei.com>, Cong Wang <xiyou.wangcong@...il.com>, "weiyongjun (A)" <weiyongjun1@...wei.com>, Eric Dumazet <eric.dumazet@...il.com> Subject: [PATCH net V2] tuntap: synchronize through tfiles array instead of tun->numqueues When a queue(tfile) is detached through __tun_detach(), we move the last enabled tfile to the position where detached one sit but don't NULL out last position. We expect to synchronize the datapath through tun->numqueues. Unfortunately, this won't work since we're lacking sufficient mechanism to order or synchronize the access to tun->numqueues. To fix this, NULL out the last position during detaching and check RCU protected tfile against NULL instead of checking tun->numqueues in datapath. Cc: YueHaibing <yuehaibing@...wei.com> Cc: Cong Wang <xiyou.wangcong@...il.com> Cc: weiyongjun (A) <weiyongjun1@...wei.com> Cc: Eric Dumazet <eric.dumazet@...il.com> Fixes: c8d68e6be1c3b ("tuntap: multiqueue support") Signed-off-by: Jason Wang <jasowang@...hat.com> --- Changes from V1: - keep the check in tun_xdp_xmit() --- drivers/net/tun.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index e9ca1c0..32a0b23 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -700,6 +700,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean) tun->tfiles[tun->numqueues - 1]); ntfile = rtnl_dereference(tun->tfiles[index]); ntfile->queue_index = index; + rcu_assign_pointer(tun->tfiles[tun->numqueues - 1], + NULL); --tun->numqueues; if (clean) { @@ -1082,7 +1084,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev) tfile = rcu_dereference(tun->tfiles[txq]); /* Drop packet if interface is not attached */ - if (txq >= tun->numqueues) + if (!tfile) goto drop; if (!rcu_dereference(tun->steering_prog)) @@ -1313,6 +1315,10 @@ static int tun_xdp_xmit(struct net_device *dev, int n, tfile = rcu_dereference(tun->tfiles[smp_processor_id() % numqueues]); + if (!tfile) { + rcu_read_unlock(); + return -ENXIO; /* Caller will free/return all frames */ + } spin_lock(&tfile->tx_ring.producer_lock); for (i = 0; i < n; i++) { -- 1.8.3.1
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