linux-kernel - Re: [LKP] Re: [mm/debug] fa6726c1e7: kernel_BUG_at

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Date:   Wed, 29 Apr 2020 20:52:25 +0800
From:   "Chen, Rong A" <rong.a.chen@...el.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Qian Cai <cai@....pw>
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        kernel test robot <lkp@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Ingo Molnar <mingo@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Will Deacon <will@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org
Subject: Re: [LKP] Re: [mm/debug] fa6726c1e7: kernel_BUG_at_include/linux/mm.h



On 4/29/2020 11:28 AM, Anshuman Khandual wrote:
>
> On 04/28/2020 02:51 PM, Catalin Marinas wrote:
>> On Tue, Apr 28, 2020 at 04:41:11AM -0400, Qian Cai wrote:
>>> On Apr 28, 2020, at 1:54 AM, Anshuman Khandual <Anshuman.Khandual@....com> wrote:
>>>> That is true. There is a slight change in the rules, making it explicit yes
>>>> only when both ARCH_HAS_DEBUG_VM_PGTABLE and DEBUG_VM are enabled.
>>>>
>>>> +config DEBUG_VM_PGTABLE
>>>> +    bool "Debug arch page table for semantics compliance"
>>>> +    depends on MMU
>>>> +    depends on !IA64 && !ARM
>>>> +    depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
>>>> +    default y if ARCH_HAS_DEBUG_VM_PGTABLE && DEBUG_VM
>>>> +    help
>>>>
>>>> The default is really irrelevant as the config option can be set explicitly.
>>> That could also explain. Since not long time ago, it was only “default
>>> y if DEBUG_VM”, that caused the robot saved a .config with
>>> DEBUG_VM_PGTABLE=y by default.
>>>
>>> Even though you changed the rule recently, it has no effect as the
>>> robot could “make oldconfig” from the saved config for each linux-next
>>> tree execution and the breakage will go on.
>> I'm not entirely sure that's the case. This report still points at the
>> old commit fa6726c1e7 which has:
>>
>> +       depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
>> +       default n if !ARCH_HAS_DEBUG_VM_PGTABLE
>> +       default y if DEBUG_VM
>>
>> In -next we now have commit 647d9a0de34c and subsequently modified by
>> commit 0a8646638865. So hopefully with the latest -next tree we won't
>> see this report.
> Could some one from LKP test framework, please confirm if this still causes
> above problem on the latest linux-next by default ?

Hi,

The .config is a rand config, the problem is still exist if run "make 
oldconfig" for the config
with commit 0a8646638865.

$ grep -e CONFIG_MMU= -e CONFIG_EXPERT= -e 
CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE= -e CONFIG_DEBUG_VM= .config
CONFIG_EXPERT=y
CONFIG_MMU=y
CONFIG_DEBUG_VM=y

should we disable DEBUG_VM_PGTABLE by default?

Best Regards,
Rong Chen