| From foo@baz Sat 16 May 2020 02:04:40 PM CEST |
| From: "Michael S. Tsirkin" <mst@redhat.com> |
| Date: Thu, 7 May 2020 03:25:56 -0400 |
| Subject: virtio_net: fix lockdep warning on 32 bit |
| |
| From: "Michael S. Tsirkin" <mst@redhat.com> |
| |
| [ Upstream commit 01c3259818a11f3cc3cd767adbae6b45849c03c1 ] |
| |
| 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 |
| softirq napi context, and sometimes from a fully preemptible context, |
| but the later always runs with napi disabled. |
| |
| 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 - it doesn't know about napi being enabled/disabled. 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> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| drivers/net/virtio_net.c | 6 ++++-- |
| 1 file changed, 4 insertions(+), 2 deletions(-) |
| |
| --- a/drivers/net/virtio_net.c |
| +++ b/drivers/net/virtio_net.c |
| @@ -1231,9 +1231,11 @@ static bool try_fill_recv(struct virtnet |
| 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, flags); |
| } |
| |
| return !oom; |