Re: [PATCH 2/7] mm: introduce local state for lazy_mmu sections

[Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>]

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