| Message ID | 20200506000006.196646-1-mst@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | virtio_net: fix lockdep warning on 32 bit | expand |
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 6594aab4910e..95393b61187f 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -1243,9 +1243,11 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq, break; } while (rq->vq->num_free); if (virtqueue_kick_prepare(rq->vq) && virtqueue_notify(rq->vq)) { - u64_stats_update_begin(&rq->stats.syncp); + unsigned long flags; + + flags = u64_stats_update_begin_irqsave(&rq->stats.syncp); rq->stats.kicks++; - u64_stats_update_end(&rq->stats.syncp); + u64_stats_update_end_irqrestore(&rq->stats.syncp); } return !oom;
When we fill up a receive VQ, try_fill_recv currently tries to count kicks using a 64 bit stats counter. Turns out, on a 32 bit kernel that uses a seqcount. sequence counts are "lock" constructs where you need to make sure that writers are serialized. In turn, this means that we mustn't run two try_fill_recv concurrently. Which of course we don't. We do run try_fill_recv sometimes from a fully preemptible context and sometimes from a softirq (napi) context. However, when it comes to the seqcount, lockdep is trying to enforce the rule that the same lock isn't accessed from preemptible and softirq context. This causes a false-positive warning: WARNING: inconsistent lock state ... inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. As a work around, shut down the warning by switching to u64_stats_update_begin_irqsave - that works by disabling interrupts on 32 bit only, is a NOP on 64 bit. Reported-by: Thomas Gleixner <tglx@linutronix.de> Suggested-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- I'm not thrilled about this but this seems the best we can do for now. Completely untested. Thomas, can you pls let me know the config I need to trigger the warning in question? drivers/net/virtio_net.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)