linux-kernel - Re: [PATCH RESEND] mm/hugetlb: Don't call region_abort if region

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Message-ID: <CACT4Y+bC_AfWkG3US3f1Bkm36S+1+U2dedyJyOGN77K5joK2ZA@mail.gmail.com>
Date:   Thu, 30 Mar 2017 14:28:58 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH RESEND] mm/hugetlb: Don't call region_abort if region_chg fails

On Wed, Mar 29, 2017 at 11:17 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 29 Mar 2017 14:08:02 -0700 Mike Kravetz <mike.kravetz@...cle.com> 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.