Re: BUG in 3.19.0-rc3+

[Chris Clayton]

Thanks Konstantin.

[snip]

>>>
>>> Looks like degree (%edx) is 1 on anon-vma desruction.
>>> Probably I've overlooked some weird conrner case in vma splitting/merging.
>>>
>>> Could you try this patch. It disables vma merging end eliminates half
>>> of complicated paths.
>>> As I see merging is optional, everything should work fine without it.
>>>
>>> --- a/mm/mmap.c
>>> +++ b/mm/mmap.c
>>> @@ -1048,7 +1048,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>>>          * We later require that vma->vm_flags == vm_flags,
>>>          * so this tests vma->vm_flags & VM_SPECIAL, too.
>>>          */
>>> -       if (vm_flags & VM_SPECIAL)
>>> +       if (1)
>>>                 return NULL;
>>>
>>>         if (prev)
>>>
>>>
>>>
>>>
>>> Code from your oops.
>>>
>>> Code: 00 ad de 48 89 43 18 e8 c5 f9 00 00 48 8b 45 10 48 8d 55 10 48
>>> 83 e8 10 49 39 d6 74 54 48 8b 7d 08 48 89 eb 8b 57 34 85 d2 74 9e <0f>
>>> 0b 0f 1f 40 00 e8 6b fc ff ff eb 9a 66 0f 1f 84 00 00 00 00
>>> All code
>>> ========
>>>    0: 00 ad de 48 89 43     add    %ch,0x438948de(%rbp)
>>>    6: 18 e8                 sbb    %ch,%al
>>>    8: c5 f9 00             (bad)
>>>    b: 00 48 8b             add    %cl,-0x75(%rax)
>>>    e: 45 10 48 8d           adc    %r9b,-0x73(%r8)
>>>   12: 55                   push   %rbp
>>>   13: 10 48 83             adc    %cl,-0x7d(%rax)
>>>   16: e8 10 49 39 d6       callq  0xffffffffd639492b
>>>   1b: 74 54                 je     0x71
>>>   1d: 48 8b 7d 08           mov    0x8(%rbp),%rdi
>>>   21: 48 89 eb             mov    %rbp,%rbx
>>>   24: 8b 57 34             mov    0x34(%rdi),%edx
>>>   27: 85 d2                 test   %edx,%edx
>>>   29: 74 9e                 je     0xffffffffffffffc9
>>>   2b:* 0f 0b                 ud2     <-- trapping instruction
>>>   2d: 0f 1f 40 00           nopl   0x0(%rax)
>>>   31: e8 6b fc ff ff       callq  0xfffffffffffffca1
>>>   36: eb 9a                 jmp    0xffffffffffffffd2
>>>   38: 66                   data16
>>>   39: 0f                   .byte 0xf
>>>   3a: 1f                   (bad)
>>>   3b: 84 00                 test   %al,(%rax)
>>>   3d: 00 00                 add    %al,(%rax)
>>> ...
>>>
>>> Code starting with the faulting instruction
>>> ===========================================
>>>    0: 0f 0b                 ud2
>>>    2: 0f 1f 40 00           nopl   0x0(%rax)
>>>    6: e8 6b fc ff ff       callq  0xfffffffffffffc76
>>>    b: eb 9a                 jmp    0xffffffffffffffa7
>>>    d: 66                   data16
>>>    e: 0f                   .byte 0xf
>>>    f: 1f                   (bad)
>>>   10: 84 00                 test   %al,(%rax)
>>>   12: 00 00                 add    %al,(%rax)
>>>
>>>
>>> +Added Oded Gabbay <oded.gabbay@xxxxxxx> into cc, he's reported this
>>> problem too.
>>>
>> Thanks for the fast reply.
>>
>> I applied the patch and tested it. I wasn't able to reproduce *my* problem,
>> so you are definitely in the right direction :)
> 
> Ok. I've found something. Try patch from attachment.
> 

Your patch has fixed the BUG for me. Thank you.

Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx>

>>
>>         Oded
>>
>>>>
>>>> In case it helps, I've attached the xz-compressed related config file.
>>>>
>>>> Chris
>>>>
>>>>>
>>>>> I've attached the full kernel log file for that boot.
>>>>>
>>>>> Chris
>>>>>
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