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

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Message-ID: <20231019022902.GA344723@monkey>
Date:   Wed, 18 Oct 2023 19:29:02 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     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 10/19/23 11:15, Sergey Senozhatsky wrote:
> 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

Thank you for testing!
-- 
Mike Kravetz