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Subject: Re: [PATCH] hugetlb: Fix __prep_compound_gigantic_page page flag
 setting
From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20221118195249.178319-1-mike.kravetz@oracle.com>
Date:   Sun, 20 Nov 2022 12:03:52 +0800
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Joao Martins <joao.m.martins@oracle.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>, Peter Xu <peterx@redhat.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Oscar Salvador <osalvador@suse.de>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Vlastimil Babka <vbabka@kernel.org>,
        Sidhartha Kumar <sidhartha.kumar@oracle.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
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Message-Id: <2D335332-2BFB-4F69-ACA2-3CE5EC5BD494@linux.dev>
References: <20221118195249.178319-1-mike.kravetz@oracle.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Precedence: bulk


> On Nov 19, 2022, at 03:52, Mike Kravetz <mike.kravetz@oracle.com> =
wrote:
>=20
> 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:
>=20
>    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.
>=20
> Make sure to __ClearPageReserved BEFORE __SetPageHead.
>=20
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating =
hugetlb pages")
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Muchun Song <songmuchun@bytedance.com>

Thanks.