linux-kernel - Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers

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Message-ID: <c022e863-0807-fab1-cd41-3c320381f448@c-s.fr>
Date:   Wed, 4 Mar 2020 07:48:54 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Qian Cai <cai@....pw>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Catalin Marinas <catalin.marinas@....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>,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390@...r.kernel.org, linux-riscv@...ts.infradead.org,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-arch@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH V14] mm/debug: Add tests validating architecture page
 table helpers



Le 04/03/2020 à 02:39, Qian Cai a écrit :
> 
>> Below is slightly modified version of your change above and should still
>> prevent the bug on powerpc. Will it be possible for you to re-test this
>> ? Once confirmed, will send a patch enabling this test on powerpc64
>> keeping your authorship. Thank you.
> 
> This works fine on radix MMU but I decided to go a bit future to test hash
> MMU. The kernel will stuck here below. I did confirm that pte_alloc_map_lock()
> was successful, so I don’t understand hash MMU well enough to tell why
> it could still take an interrupt at pte_clear_tests() even before we calls
> pte_unmap_unlock()?

AFAIU, you are not taking an interrupt here. You are stuck in the 
pte_update(), most likely due to nested locks. Try with LOCKDEP ?

Christophe

> 
> [   33.881515][    T1] ok 8 - property-entry
> [   33.883653][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [   60.418885][    C8] watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
> [swapper/0:1]