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Date: Wed, 06 Feb 2008 06:44:23 -0500
From: Jeff Garzik <jeff@...zik.org>
To: Christian Borntraeger <borntraeger@...ibm.com>
CC: Rusty Russell <rusty@...tcorp.com.au>, netdev@...r.kernel.org,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_net: Fix open <-> interrupt race
Christian Borntraeger wrote:
> Jeff,
>
> Rusty is (supposed to be) on vacation. Can you send this fix against
> virtio_net with your next network driver fixes for 2.6.25?
>
> Thank you
>
> -
>
> I got the following oops during interface ifup. Unfortunately its not
> easily reproducable so I cant say for sure that my fix fixes this
> problem, but I am confident and I think its correct anyway:
>
> <2>kernel BUG at /space/kvm/drivers/virtio/virtio_ring.c:234!
> <4>illegal operation: 0001 [#1] PREEMPT SMP
> <4>Modules linked in:
> <4>CPU: 0 Not tainted 2.6.24zlive-guest-07293-gf1ca151-dirty #91
> <4>Process swapper (pid: 0, task: 0000000000800938, ksp: 000000000084ddb8)
> <4>Krnl PSW : 0404300180000000 0000000000466374 (vring_disable_cb+0x30/0x34)
> <4> R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:0 CC:3 PM:0 EA:3
> <4>Krnl GPRS: 0000000000000001 0000000000000001 0000000010003800 0000000000466344
> <4> 000000000e980900 00000000008848b0 000000000084e748 0000000000000000
> <4> 000000000087b300 0000000000001237 0000000000001237 000000000f85bdd8
> <4> 000000000e980920 00000000001137c0 0000000000464754 000000000f85bdd8
> <4>Krnl Code: 0000000000466368: e3b0b0700004 lg %r11,112(%r11)
> <4> 000000000046636e: 07fe bcr 15,%r14
> <4> 0000000000466370: a7f40001 brc 15,466372
> <4> >0000000000466374: a7f4fff6 brc 15,466360
> <4> 0000000000466378: eb7ff0500024 stmg %r7,%r15,80(%r15)
> <4> 000000000046637e: a7f13e00 tmll %r15,15872
> <4> 0000000000466382: b90400ef lgr %r14,%r15
> <4> 0000000000466386: a7840001 brc 8,466388
> <4>Call Trace:
> <4>([<000201500f85c000>] 0x201500f85c000)
> <4> [<0000000000466556>] vring_interrupt+0x72/0x88
> <4> [<00000000004801a0>] kvm_extint_handler+0x34/0x44
> <4> [<000000000010d22c>] do_extint+0xbc/0xf8
> <4> [<0000000000113f98>] ext_no_vtime+0x16/0x1a
> <4> [<000000000010a182>] cpu_idle+0x216/0x238
> <4>([<000000000010a162>] cpu_idle+0x1f6/0x238)
> <4> [<0000000000568656>] rest_init+0xaa/0xb8
> <4> [<000000000084ee2c>] start_kernel+0x3fc/0x490
> <4> [<0000000000100020>] _stext+0x20/0x80
> <4>
> <4> <0>Kernel panic - not syncing: Fatal exception in interrupt
> <4>
>
> After looking at the code and the dump I think the following scenario
> happened: Ifup was running on cpu2 and the interrupt arrived on cpu0.
> Now virtnet_open on cpu 2 managed to execute napi_enable and disable_cb
> but did not execute rx_schedule. Meanwhile on cpu 0 skb_recv_done was
> called by vring_interrupt, executed netif_rx_schedule_prep, which
> succeeded and therefore called disable_cb. This triggered the BUG_ON,
> as interrupts were already disabled by cpu 2.
>
> I think the proper solution is to make the call to disable_cb depend on
> the atomic update of NAPI_STATE_SCHED by using netif_rx_schedule_prep
> in the same way as skb_recv_done.
>
>
> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> Acked-by: Rusty Russell <rusty@...tcorp.com.au>
>
> ---
> drivers/net/virtio_net.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> Index: kvm/drivers/net/virtio_net.c
> ===================================================================
> --- kvm.orig/drivers/net/virtio_net.c
> +++ kvm/drivers/net/virtio_net.c
> @@ -321,10 +321,12 @@ static int virtnet_open(struct net_devic
>
> /* If all buffers were filled by other side before we napi_enabled, we
> * won't get another interrupt, so process any outstanding packets
> - * now. virtnet_poll wants re-enable the queue, so we disable here. */
> - vi->rvq->vq_ops->disable_cb(vi->rvq);
> - netif_rx_schedule(vi->dev, &vi->napi);
> -
> + * now. virtnet_poll wants re-enable the queue, so we disable here.
> + * We synchronize against interrupts via NAPI_STATE_SCHED */
> + if (netif_rx_schedule_prep(dev, &vi->napi)) {
> + vi->rvq->vq_ops->disable_cb(vi->rvq);
> + __netif_rx_schedule(dev, &vi->napi);
> + }
> return 0;
> }
applied
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