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

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Message-ID: <75db1f58-98b3-463c-af4f-2ce9878cba9f@arm.com>
Date: Fri, 5 Sep 2025 00:14:39 +0200
From: Kevin Brodsky <kevin.brodsky@....com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
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 <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 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?

- Kevin