From 36ccdf85829a7dd6936dba5d02fa50138471f0d3 Mon Sep 17 00:00:00 2001 From: Björn Töpel Date: Mon, 23 Nov 2020 18:56:00 +0100 Subject: net, xsk: Avoid taking multiple skbuff references MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit 642e450b6b59 ("xsk: Do not discard packet when NETDEV_TX_BUSY") addressed the problem that packets were discarded from the Tx AF_XDP ring, when the driver returned NETDEV_TX_BUSY. Part of the fix was bumping the skbuff reference count, so that the buffer would not be freed by dev_direct_xmit(). A reference count larger than one means that the skbuff is "shared", which is not the case. If the "shared" skbuff is sent to the generic XDP receive path, netif_receive_generic_xdp(), and pskb_expand_head() is entered the BUG_ON(skb_shared(skb)) will trigger. This patch adds a variant to dev_direct_xmit(), __dev_direct_xmit(), where a user can select the skbuff free policy. This allows AF_XDP to avoid bumping the reference count, but still keep the NETDEV_TX_BUSY behavior. Fixes: 642e450b6b59 ("xsk: Do not discard packet when NETDEV_TX_BUSY") Reported-by: Yonghong Song Signed-off-by: Björn Töpel Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20201123175600.146255-1-bjorn.topel@gmail.com --- net/core/dev.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'net/core/dev.c') diff --git a/net/core/dev.c b/net/core/dev.c index 82dc6b48e45f..8588ade790cb 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4180,7 +4180,7 @@ int dev_queue_xmit_accel(struct sk_buff *skb, struct net_device *sb_dev) } EXPORT_SYMBOL(dev_queue_xmit_accel); -int dev_direct_xmit(struct sk_buff *skb, u16 queue_id) +int __dev_direct_xmit(struct sk_buff *skb, u16 queue_id) { struct net_device *dev = skb->dev; struct sk_buff *orig_skb = skb; @@ -4210,17 +4210,13 @@ int dev_direct_xmit(struct sk_buff *skb, u16 queue_id) dev_xmit_recursion_dec(); local_bh_enable(); - - if (!dev_xmit_complete(ret)) - kfree_skb(skb); - return ret; drop: atomic_long_inc(&dev->tx_dropped); kfree_skb_list(skb); return NET_XMIT_DROP; } -EXPORT_SYMBOL(dev_direct_xmit); +EXPORT_SYMBOL(__dev_direct_xmit); /************************************************************************* * Receiver routines -- cgit v1.2.3