linux-kernel - Re: [linus:master] [hugetlb] 7118fc2906: kernel_BUG_at_lib/list

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Message-ID: <94f49d5f-9e57-68c0-8c86-36a790c7c729@intel.com>
Date:   Tue, 17 Jan 2023 15:47:04 +0800
From:   "Yin, Fengwei" <fengwei.yin@...el.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        kernel test robot <oliver.sang@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
CC:     <oe-lkp@...ts.linux.dev>, <lkp@...el.com>,
        <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>,
        Youquan Song <youquan.song@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jan Kara <jack@...e.cz>, John Hubbard <jhubbard@...dia.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Matthew Wilcox" <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Feng Tang <feng.tang@...el.com>
Subject: Re: [linus:master] [hugetlb] 7118fc2906:
 kernel_BUG_at_lib/list_debug.c



On 1/17/2023 3:39 PM, Vlastimil Babka wrote:
> So either the assumption of refcount being already 0 is wrong (shouldn't be,
> AFAIK?), or this atomic operation effectively prevents some very subtle race
> (although IIRC atomic_set() has no barrier semantics defined, it could still
> affect a specific CPU?
Is there difference of atomic_set() for 32bit and 64bit? This issue is only
triggered on 32bit configuration.

> 
> I guess we could
> - try to restore that set_page_count(p, 0); on current kernel to see if it
> kills the bug
I tried this. But didn't try too hard. 20 times reboot didn't trigger the issue
with this line added to commit 0af8489b02.

Without this line, hit the issue 4 times in 10 times reboot testing.


Regards
Yin, Fengwei