linux-kernel - Re: [External] [PATCH 0/2] Track reserve map changes to restore on error

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Message-ID: <1485e64d-e794-c24e-9688-51b0c1bc1340@oracle.com>
Date:   Wed, 26 May 2021 10:17:05 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Mina Almasry <almasrymina@...gle.com>,
        Linux-MM <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [External] [PATCH 0/2] Track reserve map changes to restore on
 error

On 5/25/21 8:19 PM, Muchun Song wrote:
> On Wed, May 26, 2021 at 7:31 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>
>> Here is a modification to the reservation tracking for fixup on errors.
>> It is a more general change, but should work for the hugetlb_mcopy_pte_atomic
>> case as well.
>>
>> Perhaps use this as a prerequisite for your fix(es)?  Pretty sure this
>> will eliminate the need for the call to hugetlb_unreserve_pages.
> 
> Hi Mike,
> 
> It seems like someone is fixing a bug, right? Maybe a link should be
> placed in the cover letter so that someone can know what issue
> we are facing.
> 

Thanks Muchun,

I wanted to first see if these patches would work in the code Mina is
modifying.  If this works for Mina, then a more formal patch and request
for inclusion will be sent.

I believe this issue has existed since the introduction of hugetlb
reservations in v2.6.18.  Since the bug only shows up when we take error
paths, the issue may not have been observed.  Mina found a similar issue
in an error path which could also expose this issue.
-- 
Mike Kravetz