Re: [Bugme-new] [Bug 2019] New: Bug from the mm subsystem involving X (fwd)

["Martin J. Bligh" <mbligh@aracnet.com>]

>> So there have been alot of X issue with Red Hat and 2.6 kernels.  I managed to
>> get the system to panic and I decide it was time to open this bug.  I got this
>> on boot up. 
> 
> Hmm. Compiler? Why would AS-3 in particular have problems?

I think it's more likely the combination of NUMA and X. People hardly
ever run X on the big servers ... Keith is just odd ;-)
 
>> Unable to handle kernel paging request at virtual address 0264d000
>>  printing eip:
>> c0147af4
>> *pde = 00000000
>> Oops: 0000 [#1]
>> CPU:    7
>> EIP:    0060:[<c0147af4>]    Not tainted
>> EFLAGS: 00013206
>> EIP is at remap_page_range+0x193/0x26c
>> eax: 0264d000   ebx: 000f5200   ecx: 00000001   edx: dad0fa80
>> esi: 001fe000   edi: d87c9ff0   ebp: f5200000   esp: d8835ee4
>> ds: 007b   es: 007b   ss: 0068
>> Process X (pid: 1285, threadinfo=d8834000 task=d9474ce0)
>> Stack: d961d580 001ff000 001ff000 40000000 f5002000 001fe000 d9578000 d961d580
>>        401ff000 d9576508 00000000 f5200000 d961d580 00000001 c0247055 d87d62c0
>>        401fe000 b5002000 00001000 00000027 d9388e80 00001000 c014a7fd d9388e80
>> Call Trace:
>>  [<c0247055>] mmap_mem+0x71/0xd4
>>  [<c014a7fd>] do_mmap_pgoff+0x362/0x70d
>>  [<c0156f65>] filp_open+0x67/0x69
>>  [<c0111c4d>] sys_mmap2+0x7a/0xaa
>>  [<c010aced>] sysenter_past_esp+0x52/0x71
>> 
>> Code: 8b 00 a9 00 08 00 00 74 10 89 d8 8b 54 24 4c c1 e8 14 09 ea
> 
> This _seems_ to be the code
> 
> 		...
>                 if (!pfn_valid(pfn) || PageReserved(pfn_to_page(pfn)))
>                         set_pte(pte, pfn_pte(pfn, prot));
> 		...
> 
> in particular, it disassembles to
> 
> 	0x8048490 <insn>:       mov    (%eax),%eax
> 	0x8048492 <insn+2>:     test   $0x800,%eax
> 	0x8048497 <insn+7>:     je     0x80484a9
> 	0x8048499 <insn+9>:     mov    %ebx,%eax
> 	0x804849b <insn+11>:    mov    0x4c(%esp,1),%edx
> 	0x804849f <insn+15>:    shr    $0x14,%eax
> 
> which seems to be the "PageReserved(pfn_to_page(pfn))" test.
> 
> This implies that you have either:
>  - a buggy "pfn_valid()" macro (do you use CONFIG_DISCONTIGMEM?)

Yup.
#define pfn_valid(pfn)          ((pfn) < num_physpages)

Which is wrong. There's a even a comment above it that says:

/*
 * pfn_valid should be made as fast as possible, and the current definition
 * is valid for machines that are NUMA, but still contiguous, which is what
 * is currently supported. A more generalised, but slower definition would
 * be something like this - mbligh:
 * ( pfn_to_pgdat(pfn) && ((pfn) < node_end_pfn(pfn_to_nid(pfn))) )
 */

;-)

Which I still don't think is correct, as there's a hole in the middle of
node 0 ... I'll make a new patch up somehow and give to Keith to test ;-)

Thanks,

M.

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