On 2018/10/17 1:55, Sebastian Andrzej Siewior wrote:
> on 32bit, lockdep notices:
> | ================================
> | WARNING: inconsistent lock state
> | 4.19.0-rc8+ #9 Tainted: G W
> | --------------------------------
> | inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> | ip/1106 [HC0[0]:SC1[1]:HE1:SE0] takes:
> | (ptrval) (&syncp->seq#2){+.?.}, at: net_rx_action+0xc8/0x380
> | {SOFTIRQ-ON-W} state was registered at:
> | lock_acquire+0x7e/0x170
> | try_fill_recv+0x5fa/0x700
> | virtnet_open+0xe0/0x180
> | __dev_open+0xae/0x130
> | __dev_change_flags+0x17f/0x200
> | dev_change_flags+0x23/0x60
> | do_setlink+0x2bb/0xa20
> | rtnl_newlink+0x523/0x830
> | rtnetlink_rcv_msg+0x14b/0x470
> | netlink_rcv_skb+0x6e/0xf0
> | rtnetlink_rcv+0xd/0x10
> | netlink_unicast+0x16e/0x1f0
> | netlink_sendmsg+0x1af/0x3a0
> | ___sys_sendmsg+0x20f/0x240
> | __sys_sendmsg+0x39/0x80
> | sys_socketcall+0x13a/0x2a0
> | do_int80_syscall_32+0x50/0x180
> | restore_all+0x0/0xb2
> | irq event stamp: 3326
> | hardirqs last enabled at (3326): [<c159e6d0>] net_rx_action+0x80/0x380
> | hardirqs last disabled at (3325): [<c159e6aa>] net_rx_action+0x5a/0x380
> | softirqs last enabled at (3322): [<c14b440d>] virtnet_napi_enable+0xd/0x60
> | softirqs last disabled at (3323): [<c101d63d>] call_on_stack+0xd/0x50
> |
> | other info that might help us debug this:
> | Possible unsafe locking scenario:
> |
> | CPU0
> | ----
> | lock(&syncp->seq#2);
> | <Interrupt>
> | lock(&syncp->seq#2);
> |
> | *** DEADLOCK ***
IIUC try_fill_recv is called only when NAPI is disabled from process
context, so there should be no point to race with virtnet_receive which
is called from NAPI handler.
I'm not sure what condition triggered this warning.
Toshiaki Makita
>
> This is the "up" path which is not a hotpath. There is also
> refill_work().
> It might be unwise to add the local_bh_disable() to try_fill_recv()
> because if it is used mostly in BH so that local_bh_en+dis might be a
> waste of cycles.
>
> Adding local_bh_disable() around try_fill_recv() for the non-BH call
> sites would render GFP_KERNEL pointless.
>
> Also, ptr->var++ is not an atomic operation even on 64bit CPUs. Which
> means if try_fill_recv() runs on CPU0 (via virtnet_receive()) then the
> worker might run on CPU1.
>
> Do we care or is this just stupid stats? Any suggestions?
>
> This warning appears since commit 461f03dc99cf6 ("virtio_net: Add kick stats").
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index dab504ec5e502..d782160cfa882 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1206,9 +1206,11 @@ 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)) {
> + local_bh_disable();
> u64_stats_update_begin(&rq->stats.syncp);
> rq->stats.kicks++;
> u64_stats_update_end(&rq->stats.syncp);
> + local_bh_enable();
> }
>
> return !oom;
>
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