开发板：友善之臂Micro2440
内 核：2.6.29
问题：使用华为EM770 modem拨号上网，用的pppd call gprs拨号，通过USB线与开发板连接，可以拨号成功。如果在拨上网之前拨叉USB不会有异常；如果拨上号后把USB线拨掉，就死机，出处内容如下：
usb 1-1: USB disconnect, address 2
Modem hangup
Connect time 2.3 minutes.
Sent 168 bytes, received 168 bytes.
Script /etc/ppp/ip-down started (pid 580)
Connection terminated.option1 ttyUSB0: GSM modem (1-port) converter now disconnected from ttyUSB0
option 1-1:1.0: device disconnected
option1 ttyUSB1: GSM modem (1-port) converter now disconnected from ttyUSB1
option 1-1:1.1: device disconnected
option1 ttyUSB2: GSM modem (1-port) converter now disconnected from ttyUSB2
option 1-1:1.2: device disconnected
[root@FriendlyARM /]#
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 17 [#1]
Modules linked in:
CPU: 0 Not tainted (2.6.29.4-FriendlyARM #16)
PC is at __rcu_process_callbacks+0x24c/0x2cc
LR is at rcu_process_callbacks+0x20/0x38
pc : [<c00652e8>] lr : [<c0065388>] psr: 60000093
sp : c03cdea0 ip : 20000013 fp : c03cdebc
r10: 0000000a r9 : 00000001 r8 : c0422440
r7 : c03cc000 r6 : c0424b44 r5 : c0424b44 r4 : c03d62b8
r3 : 00000000 r2 : ffffffff r1 : c02d4ae8 r0 : c0424b54
Flags: nZCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel
Control: c000717f Table: 33ad4000 DAC: 00000017
Process swapper (pid: 0, stack limit = 0xc03cc268)
Stack: (0xc03cdea0 to 0xc03ce000)
dea0: c03d62b8 c0424b44 00000100 c03cc000 c03cded4 c03cdec0 c0065388 c00650ac
dec0: 00000020 00000001 c03cdf0c c03cded8 c0043204 c0065378 c03d5514 c03d2c58
dee0: 0000001e 0000001e c04270d4 00000000 c0400ee4 30020414 41129200 300203e0
df00: c03cdf1c c03cdf10 c00432cc c0043198 c03cdf3c c03cdf20 c002b048 c0043294
df20: ffffffff f4000000 00004000 c0400ee4 c03cdf94 c03cdf40 c002ba44 c002b010
df40: f4100000 00000032 f4100000 60000013 c002cedc c03cc000 c002cedc c0400ee4
df60: 30020414 41129200 300203e0 c03cdf94 c03cdf98 c03cdf88 c002d4f8 c002cf3c
df80: 60000013 ffffffff c03cdfb4 c03cdf98 c002d4f8 c002ceec c0424ec4 c0400ea0
dfa0: c0021000 c03d0440 c03cdfc4 c03cdfb8 c02d0200 c002d4bc c03cdff4 c03cdfc8
dfc0: c0008930 c02d01b4 c0008470 00000000 00000000 c0021d38 00000000 c0007175
dfe0: c0400fbc c0021d34 00000000 c03cdff8 30008034 c0008740 00000000 00000000
Backtrace:
[<c006509c>] (__rcu_process_callbacks+0x0/0x2cc) from [<c0065388>] (rcu_process_callbacks+0x20/0x38)
r7:c03cc000 r6:00000100 r5:c0424b44 r4:c03d62b8
[<c0065368>] (rcu_process_callbacks+0x0/0x38) from [<c0043204>] (__do_softirq+0x7c/0xfc)
r5:00000001 r4:00000020
[<c0043188>] (__do_softirq+0x0/0xfc) from [<c00432cc>] (irq_exit+0x48/0x50)
[<c0043284>] (irq_exit+0x0/0x50) from [<c002b048>] (__exception_text_start+0x48/0x70)
[<c002b000>] (__exception_text_start+0x0/0x70) from [<c002ba44>] (__irq_svc+0x24/0xa0)
Exception stack(0xc03cdf40 to 0xc03cdf88)
df40: f4100000 00000032 f4100000 60000013 c002cedc c03cc000 c002cedc c0400ee4
df60: 30020414 41129200 300203e0 c03cdf94 c03cdf98 c03cdf88 c002d4f8 c002cf3c
df80: 60000013 ffffffff
r7:c0400ee4 r6:00004000 r5:f4000000 r4:ffffffff
[<c002cedc>] (default_idle+0x0/0xac) from [<c002d4f8>] (cpu_idle+0x4c/0x68)
[<c002d4ac>] (cpu_idle+0x0/0x68) from [<c02d0200>] (rest_init+0x5c/0x70)
r7:c03d0440 r6:c0021000 r5:c0400ea0 r4:c0424ec4
[<c02d01a4>] (rest_init+0x0/0x70) from [<c0008930>] (start_kernel+0x200/0x268)
[<c0008730>] (start_kernel+0x0/0x268) from [<30008034>] (0x30008034)
r6:c0021d34 r5:c0400fbc r4:c0007175
Code: e59f1084 e5932000 e5913000 e1e02002 (e5930000)
Kernel panic - not syncing: Fatal exception in interrupt
看样子pppd 是成功退出了，USB拔出也识别了，空指针？
看不出什么头绪，希望高手指点，有什么线索也行，谢了先
