Re: [LTP] [PATCH] max_map_count: corrected max_map_count condition

[Stanislav K. <sta...@or...>]

On 08/06/2013 10:52 AM, Stanislav Kholmanskikh wrote:
> On 08/05/2013 07:41 PM, ch...@su... wrote:
>> Hi!
> Hi, Cyril.
>>> * kernel test for max_map_count_sysctl is:
>>>      /* Too many mappings? */
>>>      if (mm->map_count > sysctl_max_map_count)
>>>        return -ENOMEM;
>> Hmm, that looks like we allow the map_count to became one greater than
>> max_map_count, is this known bug?
> I'm not sure whether this is a bug or feature but in fact mm/mmap.c contains
> this strict condition.
>
>>>     so in LTP test map_count should be greater than max_map_count by 1
>>>
>>> * only [vsyscall] is allocated without incrementing mm->map_count
>> That also looks strange, do you know why one is allocated without
>> incrementing it and another with?
>>
> [vdso] is allocated this way:
> 1) load_elf_binary (fs/binfmt_elf.c)
> 2) arch_setup_additional_pages (arch/x86/vdso/vdso32-setup.c)
> 3) install_special_mapping (mm/mmap.c)
> 4) insert_vm_struct (mm/mmap.c)
> 5) vma_link (mm/mmap.c) increases mm->map_count++
>
> I've not found where [vsyscall] may increment map_count.... Maybe it's
> by design.
> As I understand [vsyscall] was initially and intentionally implemented
> as a 'hack' - mapping functions directly to process memory space.
> On the other side [vdso], which is an elf object, and should be inserted
> in a similiar way as all shared libraries do.
> IMHO.
>
> And manual testing approves the assumption that [vdso] increments and
> [vsyscall] - doesn't.
>
> Thank you.
>
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Guys, could anybody approve or disapprove this? I'm not sure where to go 
to complete this subject.