[BUG] af_packet: tpacket_destruct_skb throws BUG under high tx load

[Daniel Borkmann <danborkmann@xxxxxxxxxxxxx>]

Under high tx load from mmap()ed PF_PACKET sockets the statement in
tpacket_destruct_skb():

  BUG_ON(__packet_get_status(po, ph) != TP_STATUS_SENDING);

is being thrown, where __packet_get_status(po, ph) has the value
TP_STATUS_SEND_REQUEST instead of TP_STATUS_SENDING.

The send(2) system call was invoked with the flag MSG_DONTWAIT. The
BUG occurred even with having dev_queue_xmit() returned successfully
in tpacket_snd().

By simply removing this BUG statement, the system seemed stable, but
this might not be the proper solution. It's reproducible and I tested
it on a multi-core system  under the latest net/net-next kernel on x86
and x86_64.

On my system, this BUG was triggered in the following cases:

* Multiple processes allocate and use a TX_RING on one device

* A single process allocates a TX_RING on one device and
/proc/sys/net/core/wmem_default, /proc/sys/net/core/wmem_max were
increased

Cheers,

Daniel
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