Re: [PATCH RESEND] mm/hugetlb: Don't call region_abort if region_chg fails

[Dmitry Vyukov]

On Wed, Mar 29, 2017 at 11:17 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 29 Mar 2017 14:08:02 -0700 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
>> Resending because of typo in Andrew's e-mail when first sent
>>
>> Changes to hugetlbfs reservation maps is a two step process.  The first
>> step is a call to region_chg to determine what needs to be changed, and
>> prepare that change.  This should be followed by a call to call to
>> region_add to commit the change, or region_abort to abort the change.
>>
>> The error path in hugetlb_reserve_pages called region_abort after a
>> failed call to region_chg.  As a result, the adds_in_progress counter
>> in the reservation map is off by 1.  This is caught by a VM_BUG_ON
>> in resv_map_release when the reservation map is freed.
>>
>> syzkaller fuzzer found this bug, that resulted in the following:
>
> I'll change the above to
>
> : syzkaller fuzzer (when using an injected kmalloc failure) found this bug,
> : that resulted in the following:
>
> it's important, because this bug won't be triggered (at all easily, at
> least) in real-world workloads.

I wonder if memory-constrained cgroups make such bugs much easier to trigger.