svn commit: r347526 - head/sys/net

[Mark Johnston]

On Mon, May 13, 2019 at 01:45:29PM +0000, Andrey V. Elsukov wrote:
> Author: ae
> Date: Mon May 13 13:45:28 2019
> New Revision: 347526
> URL: https://svnweb.freebsd.org/changeset/base/347526
> 
> Log:
>   Rework locking in BPF code to remove rwlock from fast path.
>   
>   On high packets rate the contention on rwlock in bpf_*tap*() functions
>   can lead to packets dropping. To avoid this, migrate this code to use
>   epoch(9) KPI and ConcurrencyKit's lists.
>   
>   * all lists changed to use CK_LIST;
>   * reference counting added to bpf_if and bpf_d;
>   * now bpf_if references ifnet and releases this reference on destroy;
>   * each bpf_d descriptor references bpf_if when it is attached;
>   * new struct bpf_program_buffer introduced to keep BPF filter programs;
>   * bpf_program_buffer, bpf_d and bpf_if structures are freed by
>     epoch_call();
>   * bpf_freelist and ifnet_departure event are no longer needed, thus
>     both are removed;
>   
>   Reviewed by:	melifaro
>   Sponsored by:	Yandex LLC
>   Differential Revision:	https://reviews.freebsd.org/D20224

This seems to introduce a possible recursion on the bpf cdev mutex.  Now
bpfwrite() holds the mutex over the if_output call, which may enter
bpf_mtap() via bridge_transmit(), and bpf_mtap() may attempt to
reacquire the mutex.