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authorBjörn Töpel <bjorn.topel@intel.com>2020-11-23 18:56:00 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2020-11-24 22:39:56 +0100
commit36ccdf85829a7dd6936dba5d02fa50138471f0d3 (patch)
tree9f0318f3a13070a94243d1058f6e2f32d9e29912 /net/xdp
parent178648916e73e00de83150eb0c90c0d3a977a46a (diff)
net, xsk: Avoid taking multiple skbuff references
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 <yhs@fb.com> Signed-off-by: Björn Töpel <bjorn.topel@intel.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20201123175600.146255-1-bjorn.topel@gmail.com
Diffstat (limited to 'net/xdp')
-rw-r--r--net/xdp/xsk.c8
1 files changed, 1 insertions, 7 deletions
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 5a6cdf7b320d..b7b039bd9d03 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -411,11 +411,7 @@ static int xsk_generic_xmit(struct sock *sk)
skb_shinfo(skb)->destructor_arg = (void *)(long)desc.addr;
skb->destructor = xsk_destruct_skb;
- /* Hinder dev_direct_xmit from freeing the packet and
- * therefore completing it in the destructor
- */
- refcount_inc(&skb->users);
- err = dev_direct_xmit(skb, xs->queue_id);
+ err = __dev_direct_xmit(skb, xs->queue_id);
if (err == NETDEV_TX_BUSY) {
/* Tell user-space to retry the send */
skb->destructor = sock_wfree;
@@ -429,12 +425,10 @@ static int xsk_generic_xmit(struct sock *sk)
/* Ignore NET_XMIT_CN as packet might have been sent */
if (err == NET_XMIT_DROP) {
/* SKB completed but not sent */
- kfree_skb(skb);
err = -EBUSY;
goto out;
}
- consume_skb(skb);
sent_frame = true;
}