Commit 31749468 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller

bpf: cpumap fix potential lost wake-up problem

As pointed out by Michael, commit 1c601d82 ("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: 1c601d82 ("bpf: cpumap xdp_buff to skb conversion and allocation")
Reported-by: default avatar"Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7f6b437e
...@@ -288,13 +288,17 @@ static int cpu_map_kthread_run(void *data) ...@@ -288,13 +288,17 @@ static int cpu_map_kthread_run(void *data)
/* Release CPU reschedule checks */ /* Release CPU reschedule checks */
if (__ptr_ring_empty(rcpu->queue)) { if (__ptr_ring_empty(rcpu->queue)) {
__set_current_state(TASK_INTERRUPTIBLE); set_current_state(TASK_INTERRUPTIBLE);
schedule(); /* Recheck to avoid lost wake-up */
sched = 1; if (__ptr_ring_empty(rcpu->queue)) {
schedule();
sched = 1;
} else {
__set_current_state(TASK_RUNNING);
}
} else { } else {
sched = cond_resched(); sched = cond_resched();
} }
__set_current_state(TASK_RUNNING);
/* Process packets in rcpu->queue */ /* Process packets in rcpu->queue */
local_bh_disable(); local_bh_disable();
......
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