On Fri, Sep 2, 2016 at 11:13 AM, Brenden Blanco [off-list ref] wrote:

On Mon, Aug 29, 2016 at 10:46:38AM -0700, Tom Herbert wrote:
[...]

quoted

Brenden, tracking down how the structure is freed needed a few steps,
please make sure the RCU requirements are well documented. Also, I'm

Really? It's just bpf_prog_put->call_rcu(__bpf_prog_put_rcu). I suppose
what's missing is a general guideline for which functions new consumers
of bpf should use, but I wouldn't trust myself to write such holistic
documentation accurately (e.g. interacting with nmi probes and such).

quoted

still not a fan of using xchg to set the program, seems that a lock
could be used in that path.

Where would such a lock go? Everything in mlx4/en_netdev.c relies on
rtnl, which seems sufficient and obvious...adding some new field
specific lock would be distracting and unneeded.

Just use the same mutex_lock that is already being taken in case when
priv->xdp_ring_num != xdp_ring_num. Then use normal rcu functions to
dereference and assign pointers.

Tom

quoted

Thanks,
Tom