linux-kernel - Re: Bisected: [PATCH v7 2/8] hugetlb: restructure pool allocations

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Date:   Thu, 19 Oct 2023 11:15:32 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Barry Song <21cnbao@...il.com>, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Bisected: [PATCH v7 2/8] hugetlb: restructure pool allocations

On (23/10/18 15:44), Mike Kravetz wrote:
> Hi Sergey,
> 
> Sorry for the delay.  Not ignoring your report but chasing this in
> another thread.

Hi Mike, no worries.

> https://lore.kernel.org/linux-mm/20231018222003.GA21776@monkey/

Oh, interesting.
I just read the article the other day about some of unexpected optimizations
that clang can do [1].

Setting h to NULL seems to be fixing the problem for me.

> Quick question.
> Are you using LLVM/clang in your builds?

Yes, clang 14.0.6
The kernel compiled with gcc does not BUG_ON().

> My guess is that you are hitting the same issue.  That BUG at mm/hugetlb.c:3180
> should not be checked/executed unless you allocate gigantic hugetlb pages on
> the kernel command line.  Suspect you are not doing this, and loop code is
> being run when it should not.

Looks very similar indeed.

[1] https://research.swtch.com/ub