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Subject: Re: [mm/debug] fa6726c1e7: kernel_BUG_at_include/linux/mm.h
To:     Qian Cai <cai@lca.pw>,
        Anshuman Khandual <Anshuman.Khandual@arm.com>
Cc:     kernel test robot <lkp@intel.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Ingo Molnar <mingo@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Vineet Gupta <vgupta@synopsys.com>,
        Will Deacon <will@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org
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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <b3e5d138-9e14-826c-82c9-2cec9bd41ca5@c-s.fr>
Date:   Tue, 28 Apr 2020 07:24:52 +0200
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Le 28/04/2020 à 04:51, Qian Cai a écrit :
> 
> 
>> On Apr 27, 2020, at 10:35 PM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote:
>>
>> Letting CONFIG_DEBUG_VM_PGTABLE enabled via CONFIG_EXPERT for unsupported
>> platforms i.e without ARCH_HAS_DEBUG_VM_PGTABLE, was a conscious decision
>> meant to expand it's adaptability and coverage without requiring any code
>> (i.e Kconfig) change. The easier it is to enable the test on unsupported
>> platforms right now, more folks are likely to try it out thus increasing
>> it's probability to get fixed on those platforms. That is a valid enough
>> reason to have CONFIG_EXPERT based enablement method, IMHO. Also even with
>> CONFIG_EXPERT set, CONFIG_DEBUG_VM_PGTABLE does not get enabled by default
>> automatically.
> 
> No, I am talking about PAE. There is a distinction between known broken that nobody cares (like arm32) and in-progress/unknown status (like s390).
> 
> Also, it is not very nice to introduce regressions for robots when testing PAE because they always select CONFIG__EXPERT and CONFIG_DEBUG_VM.
> 

Having CONFIG_EXPERT and CONFIG_DEBUG_VM is not enough to get 
CONFIG_DEBUG_VM_PGTABLE set to yes.

By default, CONFIG_DEBUG_VM_PGTABLE is set to no when 
ARCH_HAS_DEBUG_VM_PGTABLE is not set.

Christophe