advice on reading a call trace

[Benjamin Herrenschmidt]

On Mon, 2010-10-04 at 13:24 +0200, Jean-Mickael Guerin wrote:
> Hello,
> I'm stepping into ppc world and I'd like to know how to read this call trace,
> I enabled debug options but I'm not able to track the origin of this bug, I mean
> what happens before handle_page_fault():
> 
> Unable to handle kernel paging request for data at address 0x00000008

That's a NULL dereference

> Faulting instruction address: 0xc00abcd8
>
> [c1d0dd40] [c00ab2e4] swapin_readahead+0x34/0xbc
> [c1d0dd80] [c009e91c] handle_mm_fault+0x724/0x9b0
> [c1d0dde0] [c0014e10] do_page_fault+0x2e8/0x55c
> [c1d0df40] [c000fc8c] handle_page_fault+0xc/0x80

I suspect it's userspace before handle_page_fault(). It died with a NULL
deref in the swap code (which is strange... which kernel is this ? Do
you have out of tree patches applied ?)

Cheers,
Ben.

> Instruction dump:
> 80010034 7d435378 bb210014 38210030 7c0803a6 4e800020 7d695b78 4bffff00
> 387a007c 4847616d 38000001 7c00f830 <817b0008> 7d3c0214 7f895840 7f9ee378
> Kernel panic - not syncing: Fatal exception
> 
> Another one:
> NIP: c00b6980 LR: c00b6978 CTR: 0f9ffb20
> REGS: d6a9dc60 TRAP: 0300   Not tainted  (2.6.34.6-00392-g31e1857)
> MSR: 10029002   CR: 24004442  XER: 00000000
> DEAR: 00000008, ESR: 00000000
> TASK = da6a7440[4915] 'smrd' THREAD: d6a9c000 CPU: 0
> GPR00: 00000008 d6a9dd10 da6a7440 c0738340 00000000 00000000 00000000 00000001
> GPR08: 00000000 00000000 c00b6978 00000000 44004442 10027f04 c077790c d79f94a8
> GPR16: d6a9dd88 c07a0000 d72301f0 d6a9c000 000001ff 00000000 0f9ffb20 da5c6f78
> GPR24: d79f9440 c0738340 d6a9dd48 00000000 07832400 00000001 00000003 07832400
> NIP [c00b6980] valid_swaphandles+0x19c/0x1d0
> LR [c00b6978] valid_swaphandles+0x194/0x1d0
> Call Trace:
> [d6a9dd10] [c00b6978] valid_swaphandles+0x194/0x1d0 (unreliable)
> [d6a9dd40] [c00b5a10] swapin_readahead+0x34/0xbc
> [d6a9dd80] [c00a9064] handle_mm_fault+0x7c0/0x868
> [d6a9dde0] [c00158d8] do_page_fault+0x2fc/0x570
> [d6a9df40] [c001061c] handle_page_fault+0xc/0x80
> Instruction dump:
> 38210030 7c0803a6 4e800020 7d695b78 4bffff04 3d20c074 39298300 3b290040
> 7f23cb78 484843a9 38000001 7c00f030 <817b0008> 7d3f0214 7f895840 7ffdfb78
> Kernel panic - not syncing: Fatal exception
> Call Trace:
> [d6a9dba0] [c000765c] show_stack+0x40/0x15c (unreliable)
> [d6a9dbd0] [c053b780] panic+0x94/0x118
> [d6a9dc20] [c000d630] die+0x15c/0x1bc
> [d6a9dc40] [c00155a4] bad_page_fault+0x90/0xc8
> [d6a9dc50] [c001068c] handle_page_fault+0x7c/0x80
> [d6a9dd10] [c00b6978] valid_swaphandles+0x194/0x1d0
> [d6a9dd40] [c00b5a10] swapin_readahead+0x34/0xbc
> [d6a9dd80] [c00a9064] handle_mm_fault+0x7c0/0x868
> [d6a9dde0] [c00158d8] do_page_fault+0x2fc/0x570
> [d6a9df40] [c001061c] handle_page_fault+0xc/0x80
> Rebooting in 5 seconds..
> 
> Thanks,
> Jean-Mickael
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