Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 28 Apr 2020 10:21:05 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Qian Cai <cai@lca.pw>
Cc:     Anshuman Khandual <Anshuman.Khandual@arm.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        kernel test robot <lkp@intel.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        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
Subject: Re: [mm/debug] fa6726c1e7: kernel_BUG_at_include/linux/mm.h
Message-ID: <20200428092105.GB3868@gaia>
References: <9e9091b9-6918-d0af-dd92-3bdc0e29a4d5@arm.com>
 <813D7CD3-F31C-4056-92DF-D462633E9D69@lca.pw>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <813D7CD3-F31C-4056-92DF-D462633E9D69@lca.pw>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@arm.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.

We could as well remove the 'depends on ... || EXPERT' part but I'd
rather leave this around with a default n (as in current -next) in case
others want to have a go. If that's still causing problems, we can
remove the '|| EXPERT' part, so there won't be any further regressions.

-- 
Catalin