From 9871a9e47a2646fe30ae7fd2e67668a8d30912f6 Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Wed, 8 May 2019 23:20:18 -0400
Subject: [PATCH] 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@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: weiyongjun (A) <weiyongjun1@huawei.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
drivers/net/tun.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a52bd47e7aa20..abae165dcca5a 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -704,6 +704,8 @@ 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) {
@@ -1086,7 +1088,7 @@ 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))
@@ -1309,6 +1311,7 @@ static int tun_xdp_xmit(struct net_device *dev, int n,
rcu_read_lock();
+resample:
numqueues = READ_ONCE(tun->numqueues);
if (!numqueues) {
rcu_read_unlock();
@@ -1317,6 +1320,8 @@ static int tun_xdp_xmit(struct net_device *dev, int n,
tfile = rcu_dereference(tun->tfiles[smp_processor_id() %
numqueues]);
+ if (unlikely(!tfile))
+ goto resample;
spin_lock(&tfile->tx_ring.producer_lock);
for (i = 0; i < n; i++) {
--
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