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

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Message-ID: <73189e81-08c2-bb18-dd4a-f717996ea819@redhat.com>
Date:   Wed, 16 Nov 2022 10:08:27 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Liu Shixin <liushixin2@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.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 2/2] arm64/mm: fix incorrect file_map_count for invalid
 pmd/pud

On 16.11.22 09:38, Liu Shixin wrote:
> The page table check trigger BUG_ON() unexpectedly when split hugepage:
> 
>   ------------[ cut here ]------------
>   kernel BUG at mm/page_table_check.c:119!
>   Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>   Dumping ftrace buffer:
>      (ftrace buffer empty)
>   Modules linked in:
>   CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748
>   Hardware name: linux,dummy-virt (DT)
>   pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>   pc : page_table_check_set.isra.0+0x398/0x468
>   lr : page_table_check_set.isra.0+0x1c0/0x468
> [...]
>   Call trace:
>    page_table_check_set.isra.0+0x398/0x468
>    __page_table_check_pte_set+0x160/0x1c0
>    __split_huge_pmd_locked+0x900/0x1648
>    __split_huge_pmd+0x28c/0x3b8
>    unmap_page_range+0x428/0x858
>    unmap_single_vma+0xf4/0x1c8
>    zap_page_range+0x2b0/0x410
>    madvise_vma_behavior+0xc44/0xe78
>    do_madvise+0x280/0x698
>    __arm64_sys_madvise+0x90/0xe8
>    invoke_syscall.constprop.0+0xdc/0x1d8
>    do_el0_svc+0xf4/0x3f8
>    el0_svc+0x58/0x120
>    el0t_64_sync_handler+0xb8/0xc0
>    el0t_64_sync+0x19c/0x1a0
> [...]
> 
> On arm64, pmd_present() will return true even if the pmd is invalid.

I assume that's because of the pmd_present_invalid() check.

... I wonder why that behavior was chosen. Sounds error-prone to me.

Fix LGHTM, but I am not an arm64 pgtable expert.

-- 
Thanks,

David / dhildenb