On 2019/5/8 下午12:16, Michael S. Tsirkin wrote:
On Tue, May 07, 2019 at 12:03:36AM -0400, Jason Wang wrote:
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 <yuehaib...@huawei.com>
Cc: Cong Wang <xiyou.wangc...@gmail.com>
Cc: weiyongjun (A) <weiyongj...@huawei.com>
Cc: Eric Dumazet <eric.duma...@gmail.com>
Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
Signed-off-by: Jason Wang <jasow...@redhat.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))
Hmm don't we need to range check txq?
Looks not since tun_select_queue will always return a value which is
less than MAX_TAP_QUEUES. And we NULL out the last enabled queue in
tun_detach().
Thanks
@@ -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
