Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Subject: Re: [PATCH] hugetlb: Fix __prep_compound_gigantic_page page flag
 setting
To:     Mike Kravetz <mike.kravetz@oracle.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
CC:     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>,
        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>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20221118195249.178319-1-mike.kravetz@oracle.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <5877406c-62bb-8330-e8dc-a5d78c6ab15a@huawei.com>
Date:   Sat, 19 Nov 2022 10:05:14 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <20221118195249.178319-1-mike.kravetz@oracle.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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@linux.ibm.com>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

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

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

Thanks,
Miaohe Lin