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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] why we need call xennet_alloc_rx_buffers() in xennet_poll() in Netfront module?
On Tue, Nov 27, 2012 at 11:42:11PM -0500, David Xu wrote:
> Hi all,
>
> Why we call xennet_alloc_rx_buffers function in xennet_poll of netfront?
That is an easy answer - we need to allocate receive buffers :-)
>
> When I run the iperf benchmark to measure the TCP throughput between a
> physical machine and a VM, the TCP server which is a Xen VM crashed.
>
> I traced the source code and found that the error is from xennet_poll
> => xennet_alloc_rx_buffers => __skb_dequeue => __skb_unlink
Hm, that is rather strange that you would hit this. Is this problem
still present with the latest released kernel?
>
> 1187 static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list)
> 1188 {
> 1189 struct sk_buff *skb = skb_peek(list);
> 1190 if (skb)
> 1191 __skb_unlink(skb, list);
> 1192 return skb;
> 1193 }
>
> error is from __skb_unlinkï
>
> 1166 static inline void __skb_unlink(struct sk_buff *skb, struct
> sk_buff_head *list)
> 1167 {
> 1168 struct sk_buff *next, *prev;
> 1169
> 1170 list->qlen--;
> 1171 next = skb->next;
> 1172 prev = skb->prev;
> 1173 skb->next = skb->prev = NULL;
> 1174 next->prev = prev;
> 1175 prev->next = next;
> 1176 }
>
> in this line: next->prev = prev; I found the pointer "next" is NULL
>
> Do you know why? Thanks.
>
> [ 100.973027] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000008
> [ 100.973040] IP: [<ffffffff81455f16>] xennet_alloc_rx_buffers+0x166/0x350
> [ 100.973050] PGD 1cc98067 PUD 1d74c067 PMD 0
> [ 100.973051] Oops: 0002 [#1] SMP
> [ 100.973051] CPU 1
> [ 100.973051] Modules linked in:
> [ 100.973051]
> [ 100.973051] Pid: 9, comm: ksoftirqd/1 Not tainted 3.2.23 #131
> [ 100.973051] RIP: e030:[<ffffffff81455f16>] [<ffffffff81455f16>]
> xennet_alloc_rx_buffers+0x166/0x350
> [ 100.973051] RSP: e02b:ffff88001e8f1c10 EFLAGS: 00010206
> [ 100.973051] RAX: 0000000000000000 RBX: ffff88001da98000 RCX:
> 00000000000012b0
> [ 100.973051] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 0000000000000256
> [ 100.973051] RBP: ffff88001e8f1c60 R08: ffffc90000000000 R09:
> 0000000000017a41
> [ 100.973051] R10: 0000000000000002 R11: 0000000000017298 R12:
> ffff880019a7b700
> [ 100.973051] R13: 0000000000000256 R14: 0000000000012092 R15:
> 0000000000000092
> [ 100.973051] FS: 00007f7ace91f700(0000) GS:ffff88001fd00000(0000)
> knlGS:0000000000000000
> [ 100.973051] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 100.973051] CR2: 0000000000000008 CR3: 000000001da64000 CR4:
> 0000000000002660
> [ 100.973051] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [ 100.973051] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
> 0000000000000400
> [ 100.973051] Process ksoftirqd/1 (pid: 9, threadinfo ffff88001e8f0000,
> task ffff88001e8d7000)
> [ 100.973051] Stack:
> [ 100.973051] 0000000000000091 ffff88001da99c80 ffff88001da99400
> 0000000100012091
> [ 100.973051] ffff88001e8f1c60 000000000000002d ffff880019a8ac4e
> ffff88001fd1a590
> [ 100.973051] 0000160000000000 ffff880000000000 ffff88001e8f1db0
> ffffffff8145699a
> [ 100.973051] Call Trace:
> [ 100.973051] [<ffffffff8145699a>] xennet_poll+0x7ca/0xe80
> [ 100.973051] [<ffffffff814e3e51>] net_rx_action+0x151/0x2b0
> [ 100.973051] [<ffffffff8106090d>] __do_softirq+0xbd/0x250
> [ 100.973051] [<ffffffff81060b67>] run_ksoftirqd+0xc7/0x170
> [ 100.973051] [<ffffffff81060aa0>] ? __do_softirq+0x250/0x250
> [ 100.973051] [<ffffffff8107b0ac>] kthread+0x8c/0xa0
> [ 100.973051] [<ffffffff8167ca04>] kernel_thread_helper+0x4/0x10
> [ 100.973051] [<ffffffff81672d21>] ? retint_restore_args+0x13/0x13
> [ 100.973051] [<ffffffff8167ca00>] ? gs_change+0x13/0x13
> [ 100.973051] Code: 0f 84 19 01 00 00 83 ab 10 14 00 00 01 45 0f b6 fe 49
> 8b 14 24 49 8b 44 24 08 49 c7 04 24 00 00 00 00 49 c7 44 24 08 00 00 00 00
> <48> 89 42 08 48 89 10 41 0f b6 d7 49 89 5c 24 20 48 8d 82 b8 01
> [ 100.973051] RIP [<ffffffff81455f16>] xennet_alloc_rx_buffers+0x166/0x350
> [ 100.973051] RSP <ffff88001e8f1c10>
> [ 100.973051] CR2: 0000000000000008
> [ 100.973259] ---[ end trace b0530821c3527d70 ]---
> [ 100.973263] Kernel panic - not syncing: Fatal exception in interrupt
> [ 100.973267] Pid: 9, comm: ksoftirqd/1 Tainted: G D 3.2.23 #131
> [ 100.973270] Call Trace:
> [ 100.973273] [<ffffffff816674ae>] panic+0x91/0x1a2
> [ 100.973278] [<ffffffff8100adb2>] ? check_events+0x12/0x20
> [ 100.973282] [<ffffffff81673b0a>] oops_end+0xea/0xf0
> [ 100.973286] [<ffffffff81666e6b>] no_context+0x214/0x223
> [ 100.973291] [<ffffffff8113cf94>] ? kmem_cache_free+0x104/0x110
> [ 100.973295] [<ffffffff8166704b>] __bad_area_nosemaphore+0x1d1/0x1f0
> [ 100.973299] [<ffffffff8166707d>] bad_area_nosemaphore+0x13/0x15
> [ 100.973304] [<ffffffff816763fb>] do_page_fault+0x35b/0x4f0
> [ 100.973308] [<ffffffff814d6044>] ? __netdev_alloc_skb+0x24/0x50
> [ 100.973313] [<ffffffff8129f75a>] ? trace_hardirqs_off_thunk+0x3a/0x6c
> [ 100.973318] [<ffffffff81672fa5>] page_fault+0x25/0x30
> [ 100.973322] [<ffffffff81455f16>] ? xennet_alloc_rx_buffers+0x166/0x350
> [ 100.973326] [<ffffffff8145699a>] xennet_poll+0x7ca/0xe80
> [ 100.973330] [<ffffffff814e3e51>] net_rx_action+0x151/0x2b0
> [ 100.973334] [<ffffffff8106090d>] __do_softirq+0xbd/0x250
> [ 100.973338] [<ffffffff81060b67>] run_ksoftirqd+0xc7/0x170
> [ 100.973342] [<ffffffff81060aa0>] ? __do_softirq+0x250/0x250
> [ 100.973346] [<ffffffff8107b0ac>] kthread+0x8c/0xa0
> [ 100.973350] [<ffffffff8167ca04>] kernel_thread_helper+0x4/0x10
> [ 100.973354] [<ffffffff81672d21>] ? retint_restore_args+0x13/0x13
> [ 100.973358] [<ffffffff8167ca00>] ? gs_change+0x13/0x13
>
> Regards,
> Cong
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