linux-kernel - Re: [PATCH 2/7] mm: introduce local state for lazy

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Message-ID: <2aed0b3b-1a70-4c89-9177-8de4fabb2237@lucifer.local>
Date: Fri, 5 Sep 2025 12:21:40 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andreas Larsson <andreas@...sler.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ryan Roberts <ryan.roberts@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 2/7] mm: introduce local state for lazy_mmu sections

On Fri, Sep 05, 2025 at 12:14:39AM +0200, Kevin Brodsky wrote:
> On 04/09/2025 19:28, Lorenzo Stoakes wrote:
> > Hi Kevin,
> >
> > This is causing a build failure:
> >
> > In file included from ./include/linux/mm.h:31,
> >                  from mm/userfaultfd.c:8:
> > mm/userfaultfd.c: In function ‘move_present_ptes’:
> > ./include/linux/pgtable.h:247:41: error: statement with no effect [-Werror=unused-value]
> >   247 | #define arch_enter_lazy_mmu_mode()      (LAZY_MMU_DEFAULT)
> >       |                                         ^
> > mm/userfaultfd.c:1103:9: note: in expansion of macro ‘arch_enter_lazy_mmu_mode’
> >  1103 |         arch_enter_lazy_mmu_mode();
> >       |         ^~~~~~~~~~~~~~~~~~~~~~~~
> > ./include/linux/pgtable.h:248:54: error: expected expression before ‘)’ token
> >   248 | #define arch_leave_lazy_mmu_mode(state) ((void)(state))
> >       |                                                      ^
> > mm/userfaultfd.c:1141:9: note: in expansion of macro ‘arch_leave_lazy_mmu_mode’
> >  1141 |         arch_leave_lazy_mmu_mode();
> >       |         ^~~~~~~~~~~~~~~~~~~~~~~~
> >
> > It seems you haven't carefully checked call sites here, please do very
> > carefully recheck these - I see Yeoreum reported a mising kasan case, so I
> > suggest you just aggressively grep this + make sure you've covered all
> > bases :)
>
> I did check all call sites pretty carefully and of course build-tested,
> but my series is based on v6.17-rc4 - just like the calls Yeoreum
> mentioned, the issue is that those calls are in mm-stable but not in
> mainline :/ I suppose I should post a v2 rebased on mm-stable ASAP then?

You should really base on mm-new.

You need to account for everything that is potentially going to go
upstream. mm-stable is generally not actually populated all too well until
shortly before merge window anyway.

>
> - Kevin

Thanks, Lorenzo