Re: [net-next PATCH] bpf: cpumap fix potential lost wake-up problem

[Daniel Borkmann]

On 10/23/2017 07:39 PM, Jesper Dangaard Brouer wrote:

As pointed out by Michael, commit 1c601d829ab0 ("bpf: cpumap xdp_buff
to skb conversion and allocation") contains a classical example of the
potential lost wake-up problem.

We need to recheck the condition __ptr_ring_empty() after changing
current->state to TASK_INTERRUPTIBLE, this avoids a race between
wake_up_process() and schedule(). After this, a race with
wake_up_process() will simply change the state to TASK_RUNNING, and
the schedule() call not really put us to sleep.

Fixes: 1c601d829ab0 ("bpf: cpumap xdp_buff to skb conversion and allocation")
Reported-by: "Michael S. Tsirkin" <m...@redhat.com>

SOB missing ...