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

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Date:   Tue, 28 Apr 2020 09:23:37 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Qian Cai <cai@....pw>
Cc:     kernel test robot <lkp@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Catalin Marinas <catalin.marinas@....com>,
        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: [mm/debug] fa6726c1e7: kernel_BUG_at_include/linux/mm.h



On 04/28/2020 08:21 AM, Qian Cai wrote:
> 
> 
>> On Apr 27, 2020, at 10:35 PM, Anshuman Khandual <Anshuman.Khandual@....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.

Okay, will add X86_PAE to the explicitly disabled list along with
IA64 and ARM.

----
From: Anshuman Khandual <anshuman.khandual@....com>
Date: Tue, 28 Apr 2020 04:30:04 +0100
Subject: [PATCH 3/3] mm/debug/pgtable: Completely disable X86_PAE

Completely disable X86_PAE, even via CONFIG_EXPERT.

Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 lib/Kconfig.debug | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 6a492e32579a..79e097a2285f 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -697,7 +697,7 @@ config DEBUG_VM_PGFLAGS
 config DEBUG_VM_PGTABLE
        bool "Debug arch page table for semantics compliance"
        depends on MMU
-       depends on !IA64 && !ARM
+       depends on !IA64 && !ARM && !X86_PAE
        depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
        default y if ARCH_HAS_DEBUG_VM_PGTABLE && DEBUG_VM
        help
-- 

Hello Andrew/Stephen,

Could you please fold the above patch in linux-next. Also please do
let me know if I should respin the series as well. Thank you.

- Anshuman