Steve Deiters wrote:
>> -----Original Message-----
>> From: xenomai-help-boun...@gna.org
>> [mailto:xenomai-help-boun...@gna.org] On Behalf Of Steve Deiters
>> Sent: Friday, August 13, 2010 5:15 PM
>> To: xenomai-help@gna.org
>> Subject: [Xenomai-help] Page fault in real time task causes lockup
>>
>> I'm trying to track down a problem where it seems that a page
>> fault is causing a lockup on my machine. I am running on a
>> PowerPC with Linux version 2.6.33.5 and Xenomai 2.5.4, but
>> also saw the same thing with Xenomai 2.5.3.
>>
>> What I am doing is mmaping a FPGA on the parallel bus in my
>> task initialization. Later on I have a interrupt loop which
>> uses rt_intr_wait to service some FPGA stuff. On access to
>> some of my FPGA mapped registers I get a page fault which
>> causes a lockup. I'm guessing there is some interaction
>> going on with the rt_intr_wait and the fault exception. If I
>> prefault the map by reading some of the registers before the
>> loop it is ok. If I change the rt_intr_wait to a timed loop
>> using rt_wait_period and don't prefault the registers it is ok.
>>
>> If I enable T_WARNSW I get a SIGXCPU when it tries to access
>> the mapped registers. I don't necessarily care that it
>> faults there so I don't want to have to prefault like I am doing.
>>
>> If I enable some of the debugging options I end up with the
>> following exception dump:
>>
>> -----------
>>
>> [ 23.623184] Xenomai: Switching to secondary mode after exception
>> #769 from user-space at 0xff187ac (pid 586)
>> [ 23.634273] Xenomai: Switching to secondary mode after exception
>> #769 from user-space at 0xff187ac (pid 587)
>> [ 23.653414] Xenomai: Switching to secondary mode after exception
>> #769 from user-space at 0xff187ac (pid 592)
>> [ 23.675243] Xenomai: Switching dsp_task to secondary mode after
>> exception #769 from user-space at 0x10016634 (pid 595)
>> [ 24.456360] Xenomai: Switching dsp_task to secondary mode after
>> exception #769 from user-space at 0x10002d28 (pid 595)
>> [ 24.467285] I-pipe: Detected illicit call from domain 'Xenomai'
>> [ 24.467300] <3> into a service reserved for domain
>> 'Linux' and
>> below.
>> [ 24.480199] Xenomai: Switching dsp_task to secondary mode after
>> exception #1792 in kernel-space at 0xc0062f48 (pid 595)
>> [ 24.491109] Oops: Exception in kernel mode, sig: 5 [#1]
>> [ 24.496258] PREEMPT MPC5121 BE
>> [ 24.499300] Modules linked in: lpcmem axe immmem
>> [ 24.503912] NIP: c0062f48 LR: c0025b0c CTR: c01be5b0
>> [ 24.508870] REGS: c7bc3c60 TRAP: 0700 Not tainted (2.6.33.5)
>> [ 24.514775] MSR: 00021032 <ME,CE,IR,DR> CR: 24000422
>> XER: 20000000
>> [ 24.521127] TASK = c7b30550[595] 'dsp_task' THREAD: c7bc2000
>> [ 24.526600] GPR00: 00000001 c7bc3d10 c7b30550 c03ac1c0 00002a39
>> ffffffff c0360000 c03ac1c0
>> [ 24.534946] GPR08: 00000000 000028ff 00002900 c0360000 82000442
>> 1003c7b8 00000001 c0360000
>> [ 24.543292] GPR16: c03b0000 c7bc3f50 00008000 c0300000 c03b0000
>> c0360000 00000003 c0360000
>> [ 24.551638] GPR24: c0360000 c7bc3d3c 0000009c c7bc2000 0000000f
>> c7bc3d4b c039d918 00000001
>> [ 24.560180] NIP [c0062f48] __ipipe_unstall_root+0x34/0x80
>> [ 24.565564] LR [c0025b0c] vprintk+0x340/0x444
>> [ 24.569895] Call Trace:
>> [ 24.572336] [c7bc3d10] [c7bc3d4b] 0xc7bc3d4b (unreliable)
>> [ 24.577729] [c7bc3d20] [c0025b0c] vprintk+0x340/0x444
>> [ 24.582770] [c7bc3db0] [c0026304] printk+0xb8/0x1f8
>> [ 24.587640] [c7bc3e00] [c006256c] ipipe_check_context+0xc4/0xcc
>> [ 24.593555] [c7bc3e10] [c0299538] __down_interruptible+0xb4/0x148
>> [ 24.599643] [c7bc3e40] [c004799c] down_interruptible+0xcc/0xdc
>> [ 24.605470] [c7bc3e60] [c0075acc] xnshadow_harden+0x64/0x248
>> [ 24.611114] [c7bc3e80] [c0075d4c] losyscall_event+0x9c/0x374
>> [ 24.616766] [c7bc3ed0] [c0063bc0] __ipipe_dispatch_event+0x98/0x1f0
>> [ 24.623025] [c7bc3f20] [c000bcf0] __ipipe_syscall_root+0x60/0x170
>> [ 24.629108] [c7bc3f40] [c00133e4] DoSyscall+0x20/0x5c
>> [ 24.634151] --- Exception: c01 at 0xff19c94
>> [ 24.634158] LR = 0xff19c08
>> [ 24.641360] Instruction dump:
>> [ 24.644318] 7c0802a6 90010014 7c0000a6 5400045e 7c000124 3d60c036
>> 3d20c03b 814b2858
>> [ 24.652055] 3929c1c0 7d4a4a78 312affff 7c095110 <0f000000> 3d60c036
>> 38600000 392b14f8
>> [ 24.660058] ------------[ cut here ]------------
>> [ 24.664600] kernel BUG at kernel/ipipe/core.c:311!
>> [ 24.669413] ---[ end trace ca02c1a54b14d664 ]---
>> [ 24.674021] note: dsp_task[595] exited with preempt_count 1
>>
>
>
> If this gives any more clues, if I comment out the section in
> __rt_intr_wait in native/syscall.c where it raises the priority to
> XNSCHED_IRQ_PRIO it does not lock up.
This is strange, it looks like the thread wants to move from secondary
mode to primary mode while it is already running in primary mode.
--
Gilles.
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