linux-kernel - Re: [PATCH] hugetlb: Fix __prep_compound_gigantic

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Date:   Sat, 19 Nov 2022 10:05:14 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     Muchun Song <songmuchun@...edance.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Vlastimil Babka <vbabka@...nel.org>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] hugetlb: Fix __prep_compound_gigantic_page page flag
 setting

On 2022/11/19 3:52, Mike Kravetz wrote:
> Commit 2b21624fc232 ("hugetlb: freeze allocated pages before creating
> hugetlb pages") changed the order page flags were cleared and set in the
> head page.  It moved the __ClearPageReserved after __SetPageHead.
> However, there is a check to make sure __ClearPageReserved is never
> done on a head page.  If CONFIG_DEBUG_VM_PGFLAGS is enabled, the
> following BUG will be hit when creating a hugetlb gigantic page:
> 
>     page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
>     ------------[ cut here ]------------
>     kernel BUG at include/linux/page-flags.h:500!
>     Call Trace will differ depending on whether hugetlb page is created
>     at boot time or run time.
> 
> Make sure to __ClearPageReserved BEFORE __SetPageHead.
> 
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Yes, PG_reserved is PF_NO_COMPOUND policy. Thanks for fixing this.

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks,
Miaohe Lin