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authorJesper Dangaard Brouer <brouer@redhat.com>2017-10-23 19:39:28 +0200
committerDavid S. Miller <davem@davemloft.net>2017-10-24 18:40:22 +0900
commit31749468c3f9d77927ed3144259dc208e6625ede (patch)
tree33d083824b454cd344121d6ef8ed2ac1d37afeb4 /kernel
parent7f6b437e9b82a6d702a7f8f75c83ffdec6e03c54 (diff)
downloadlinux-31749468c3f9d77927ed3144259dc208e6625ede.tar.bz2
bpf: cpumap fix potential lost wake-up problem
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/cpumap.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index b4358d84ddf1..86e29cbf7827 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -288,13 +288,17 @@ static int cpu_map_kthread_run(void *data)
/* 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();