Re: [PATCH net-next V4 0/6] switch to use tx skb array in tun

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 06, 2016 at 01:45:58PM -0400, Craig Gallek wrote:
> On Thu, Jun 30, 2016 at 2:45 AM, Jason Wang <jasowang@redhat.com> wrote:
> > Hi all:
> >
> > This series tries to switch to use skb array in tun. This is used to
> > eliminate the spinlock contention between producer and consumer. The
> > conversion was straightforward: just introdce a tx skb array and use
> > it instead of sk_receive_queue.
> 
> I'm seeing the splat below after this series.  I'm still wrapping my
> head around this code, but it appears to be happening because the
> tun_struct passed into tun_queue_resize is uninitialized.
> Specifically, iteration over the disabled list_head fails because prev
> = next = NULL.  This seems to happen when a startup script on my test
> machine changes the queue length.  I'll try to figure out what's
> happening, but if it's obvious to someone else from the stack, please
> let me know.


Don't see anything obvious. I'm traveling, will look at it when I'm back
unless it's fixed by then. Jason, any idea?

> [   72.322236] BUG: unable to handle kernel NULL pointer dereference
> at 0000000000000010
> [   72.329993] IP: [<ffffffff8153c1a0>] tun_device_event+0x110/0x340
> [   72.336032] PGD 7f054f1067 PUD 7ef6f3f067 PMD 0
> [   72.340616] Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
> [   72.345498] gsmi: Log Shutdown Reason 0x03
> [   72.349541] Modules linked in: w1_therm wire cdc_acm ehci_pci
> ehci_hcd mlx4_en ib_uverbs mlx4_ib ib_core mlx4_core
> [   72.359870] CPU: 12 PID: 7820 Comm: set.ixion-haswe Not tainted
> 4.7.0-dbx-DEV #10
> [   72.360253] mlx4_en: eth0: Link Up
> [   72.370618] Hardware name: Intel Grantley,Wellsburg/Ixion_IT_15,
> BIOS 2.50.0 01/21/2016
> [   72.378525] task: ffff883f2501e8c0 ti: ffff883f3ef08000 task.ti:
> ffff883f3ef08000
> [   72.385917] RIP: 0010:[<ffffffff8153c1a0>]  [<ffffffff8153c1a0>]
> tun_device_event+0x110/0x340
> [   72.394353] RSP: 0018:ffff883f3ef0bbe8  EFLAGS: 00010202
> [   72.399599] RAX: fffffffffffffae8 RBX: ffff887ef9883378 RCX: 0000000000000000
> [   72.406647] RDX: 0000000000000000 RSI: 0000000000000028 RDI: 0000000000000000
> [   72.413694] RBP: ffff883f3ef0bc58 R08: 0000000000000000 R09: 0000000000000001
> [   72.420742] R10: 0000000000000004 R11: 0000000000000000 R12: 0000000000000010
> [   72.427789] R13: 0000000000000000 R14: 0000000000000001 R15: ffff883f3ef0bd10
> [   72.434837] FS:  00007fac4e5dd700(0000) GS:ffff883f7f700000(0000)
> knlGS:0000000000000000
> [   72.442832] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   72.448507] CR2: 0000000000000010 CR3: 0000007ef66ac000 CR4: 00000000001406e0
> [   72.455555] Stack:
> [   72.457541]  ffff883f3ef0bc18 0000000000000246 000000000000001e
> ffff887ef9880000
> [   72.464880]  ffff883f3ef0bd10 0000000000000000 0000000000000000
> ffffffff00000000
> [   72.472219]  ffff883f3ef0bc58 ffffffff81d24070 00000000fffffff9
> ffffffff81cec7a0
> [   72.479559] Call Trace:
> [   72.481986]  [<ffffffff810eeb0d>] notifier_call_chain+0x5d/0x80
> [   72.487844]  [<ffffffff816365c0>] ? show_tx_maxrate+0x30/0x30
> [   72.493520]  [<ffffffff810eeb3e>] __raw_notifier_call_chain+0xe/0x10
> [   72.499801]  [<ffffffff810eeb56>] raw_notifier_call_chain+0x16/0x20
> [   72.506001]  [<ffffffff8160eb30>] call_netdevice_notifiers_info+0x40/0x70
> [   72.512706]  [<ffffffff8160ec36>] call_netdevice_notifiers+0x16/0x20
> [   72.518986]  [<ffffffff816365f8>] change_tx_queue_len+0x38/0x80
> [   72.524838]  [<ffffffff816381cf>] netdev_store.isra.5+0xbf/0xd0
> [   72.530688]  [<ffffffff81638330>] tx_queue_len_store+0x50/0x60
> [   72.536459]  [<ffffffff814a6798>] dev_attr_store+0x18/0x30
> [   72.541888]  [<ffffffff812ea3ff>] sysfs_kf_write+0x4f/0x70
> [   72.547306]  [<ffffffff812e9507>] kernfs_fop_write+0x147/0x1d0
> [   72.553077]  [<ffffffff81134a4f>] ? rcu_read_lock_sched_held+0x8f/0xa0
> [   72.559534]  [<ffffffff8125a108>] __vfs_write+0x28/0x120
> [   72.564781]  [<ffffffff8111b137>] ? percpu_down_read+0x57/0x90
> [   72.570542]  [<ffffffff8125d7d8>] ? __sb_start_write+0xc8/0xe0
> [   72.576303]  [<ffffffff8125d7d8>] ? __sb_start_write+0xc8/0xe0
> [   72.582063]  [<ffffffff8125bd5e>] vfs_write+0xbe/0x1b0
> [   72.587138]  [<ffffffff8125c092>] SyS_write+0x52/0xa0
> [   72.592135]  [<ffffffff817528a5>] entry_SYSCALL_64_fastpath+0x18/0xa8
> [   72.598497] Code: 45 31 f6 48 8b 93 78 33 00 00 48 81 c3 78 33 00
> 00 48 39 d3 48 8d 82 e8 fa ff ff 74 25 48 8d b0 40 05 00 00 49 63 d6
> 41 83 c6 01 <49> 89 34 d4 48 8b 90 18 05 00 00 48 39 d3 48 8d 82 e8 fa
> ff ff
> [   72.617767] RIP  [<ffffffff8153c1a0>] tun_device_event+0x110/0x340
> [   72.623883]  RSP <ffff883f3ef0bbe8>
> [   72.627327] CR2: 0000000000000010
> [   72.630638] ---[ end trace b0c54137cf861b91 ]---