Re: mm: kernel BUG at mm/mlock.c:82!

[Sasha Levin <sasha.levin@oracle.com>]

On 12/17/2013 12:39 AM, Bob Liu wrote:
> cc'd more people.
>
> On 12/17/2013 09:04 AM, Sasha Levin wrote:
>> Hi all,
>>
>> While fuzzing with trinity inside a KVM tools guest running latest -next
>> kernel, I've
>> stumbled on the following spew.
>>
>> Codewise, it's pretty straightforward. In try_to_unmap_cluster():
>>
>>                  page = vm_normal_page(vma, address, *pte);
>>                  BUG_ON(!page || PageAnon(page));
>>
>>                  if (locked_vma) {
>>                          mlock_vma_page(page);   /* no-op if already
>> mlocked */
>>                          if (page == check_page)
>>                                  ret = SWAP_MLOCK;
>>                          continue;       /* don't unmap */
>>                  }
>>
>> And the BUG triggers once we see that 'page' isn't locked.
>>
>
> Yes, I didn't see any place locked the corresponding page in
> try_to_unmap_cluster().
>
> I'm afraid adding lock_page() over there may cause potential deadlock.
> How about just remove the BUG_ON() in mlock_vma_page()?

Welp, it's been there for 5 years now - there should be a good reason to justify removing it.


Thanks,
Sasha

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