linux-kernel - Re: [PATCH v2 1/2] arm64/mm: fix incorrect file_map

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Message-ID: <65ca8d04-d7cc-cdb3-1dab-034b9e37a12c@huawei.com>
Date:   Thu, 17 Nov 2022 15:56:15 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Liu Shixin <liushixin2@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        "David Hildenbrand" <dhildenb@...hat.com>,
        Rafael Aquini <raquini@...hat.com>,
        "Pasha Tatashin" <pasha.tatashin@...een.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] arm64/mm: fix incorrect file_map_count for
 non-leaf pmd/pud


On 2022/11/17 15:56, Liu Shixin wrote:
> The page table check trigger BUG_ON() unexpectedly when collapse hugepage:
>
>   ------------[ cut here ]------------
>   kernel BUG at mm/page_table_check.c:82!
>   Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>   Dumping ftrace buffer:
>      (ftrace buffer empty)
>   Modules linked in:
>   CPU: 6 PID: 68 Comm: khugepaged Not tainted 6.1.0-rc3+ #750
>   Hardware name: linux,dummy-virt (DT)
>   pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>   pc : page_table_check_clear.isra.0+0x258/0x3f0
>   lr : page_table_check_clear.isra.0+0x240/0x3f0
> [...]
>   Call trace:
>    page_table_check_clear.isra.0+0x258/0x3f0
>    __page_table_check_pmd_clear+0xbc/0x108
>    pmdp_collapse_flush+0xb0/0x160
>    collapse_huge_page+0xa08/0x1080
>    hpage_collapse_scan_pmd+0xf30/0x1590
>    khugepaged_scan_mm_slot.constprop.0+0x52c/0xac8
>    khugepaged+0x338/0x518
>    kthread+0x278/0x2f8
>    ret_from_fork+0x10/0x20
> [...]
>
> Since pmd_user_accessible_page() doesn't check if a pmd is leaf, it
> decrease file_map_count for a non-leaf pmd comes from collapse_huge_page().
> and so trigger BUG_ON() unexpectedly.
>
> Fix this problem by using pmd_leaf() insteal of pmd_present() in
> pmd_user_accessible_page(). Moreover, use pud_leaf() for
> pud_user_accessible_page() too.
>
> Fixes: 42b2547137f5 ("arm64/mm: enable ARCH_SUPPORTS_PAGE_TABLE_CHECK")
> Reported-by: Denys Vlasenko <dvlasenk@...hat.com>
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Acked-by: Pasha Tatashin <pasha.tatashin@...een.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>