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 <[email protected]>
> Cc: Cong Wang <[email protected]>
> Cc: weiyongjun (A) <[email protected]>
> Cc: Eric Dumazet <[email protected]>
> Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
> Signed-off-by: Jason Wang <[email protected]>
> ---
> 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?
> @@ -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
