Re: mm: BUG in resv_map_release

[Mike Kravetz]

On 03/23/2017 10:25 AM, Mike Kravetz wrote:
> On 03/23/2017 03:19 AM, Dmitry Vyukov wrote:
>> Hello,
>>
>> I've got the following BUG while running syzkaller fuzzer.
>> Note the injected kmalloc failure, most likely it's the root cause.
> 
> Thanks  Dmitry,
> 
> The BUG indicates someone called region_chg() in the process of adding
> a hugetlbfs page reservation, but did not complete this 'two step'
> process with a call to region_add() or region_abort().  Most likely a
> missed call in an error path somewhere.  :(
> 
> I'll try to track this down.  The hint of 'injected kmalloc failure'
> should help.

Actually, in this case I believe the bug is in hugetlb_reserve_pages.
It calls region_chg(), but gets an error due to the injected kmalloc
failure.  At this point, the resv_map->adds_in_progress is 0 as it
should be.  However, the error path for hugetlb_reserve_pages calls
region_abort() which will unconditionally decrement adds_in_progress.
So, adds_in_progress goes negative and we eventually BUG.  :(

I'll look for other misuses of region_chg()/region_add()/region_abort()
and put together a patch.

Dmitry, is there some way to run the fuzzer with kmalloc failure injection
and target the hugetlbfs code?  I'm suspect we could flush out other bugs.
I noticed one other you discovered, and will look at that next.

-- 
Mike Kravetz