4.15-stable review patch. If anyone has any objections, please let me know.
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From: Jason Wang jasowang@redhat.com
[ Upstream commit 23e43f07f896f8578318cfcc9466f1e8b8ab21b6 ]
Except for tuntap, all other drivers' XDP was implemented at NAPI poll() routine in a bh. This guarantees all XDP operation were done at the same CPU which is required by e.g BFP_MAP_TYPE_PERCPU_ARRAY. But for tuntap, we do it in process context and we try to protect XDP processing by RCU reader lock. This is insufficient since CONFIG_PREEMPT_RCU can preempt the RCU reader critical section which breaks the assumption that all XDP were processed in the same CPU.
Fixing this by simply disabling preemption during XDP processing.
Fixes: 761876c857cb ("tap: XDP support") Signed-off-by: Jason Wang jasowang@redhat.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/tun.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1471,6 +1471,7 @@ static struct sk_buff *tun_build_skb(str else *skb_xdp = 0;
+ preempt_disable(); rcu_read_lock(); xdp_prog = rcu_dereference(tun->xdp_prog); if (xdp_prog && !*skb_xdp) { @@ -1494,6 +1495,7 @@ static struct sk_buff *tun_build_skb(str if (err) goto err_redirect; rcu_read_unlock(); + preempt_enable(); return NULL; case XDP_TX: xdp_xmit = true; @@ -1515,6 +1517,7 @@ static struct sk_buff *tun_build_skb(str skb = build_skb(buf, buflen); if (!skb) { rcu_read_unlock(); + preempt_enable(); return ERR_PTR(-ENOMEM); }
@@ -1527,10 +1530,12 @@ static struct sk_buff *tun_build_skb(str skb->dev = tun->dev; generic_xdp_tx(skb, xdp_prog); rcu_read_unlock(); + preempt_enable(); return NULL; }
rcu_read_unlock(); + preempt_enable();
return skb;
@@ -1538,6 +1543,7 @@ err_redirect: put_page(alloc_frag->page); err_xdp: rcu_read_unlock(); + preempt_enable(); this_cpu_inc(tun->pcpu_stats->rx_dropped); return NULL; }