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" <mst@redhat.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
/* Release CPU reschedule checks */
if (__ptr_ring_empty(rcpu->queue)) {
- __set_current_state(TASK_INTERRUPTIBLE);
- schedule();
- sched = 1;
+ set_current_state(TASK_INTERRUPTIBLE);
+ /* Recheck to avoid lost wake-up */
+ if (__ptr_ring_empty(rcpu->queue)) {
+ schedule();
+ sched = 1;
+ } else {
+ __set_current_state(TASK_RUNNING);
+ }
} else {
sched = cond_resched();
}
- __set_current_state(TASK_RUNNING);
/* Process packets in rcpu->queue */
local_bh_disable();