linux-kernel - Re: [PATCH 6.1.y] selftests/mm: Move default_huge_page_size to vm

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Message-ID: <2025102241-clubbed-smirk-8819@gregkh>
Date: Wed, 22 Oct 2025 16:26:50 +0200
From: Greg KH <greg@...ah.com>
To: Leon Hwang <leon.hwang@...ux.dev>
Cc: stable@...r.kernel.org, akpm@...ux-foundation.org, david@...hat.com,
	lorenzo.stoakes@...cle.com, shuah@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH 6.1.y] selftests/mm: Move default_huge_page_size to
 vm_util.c

On Wed, Oct 22, 2025 at 09:34:52PM +0800, Leon Hwang wrote:
> 
> 
> On 2025/10/22 16:20, Greg KH wrote:
> > On Wed, Oct 22, 2025 at 04:08:45PM +0800, Leon Hwang wrote:
> >>
> >>
> >> On 22/10/25 15:40, Greg KH wrote:
> >>> On Wed, Oct 22, 2025 at 01:51:38PM +0800, Leon Hwang wrote:
> >>>> Fix the build error:
> >>>>
> >>>> map_hugetlb.c: In function 'main':
> >>>> map_hugetlb.c:79:25: warning: implicit declaration of function 'default_huge_page_size' [-Wimplicit-function-declaration]
> >>>>    79 |         hugepage_size = default_huge_page_size();
> >>>>       |                         ^~~~~~~~~~~~~~~~~~~~~~
> >>>> /usr/bin/ld: /tmp/ccYOogvJ.o: in function 'main':
> >>>> map_hugetlb.c:(.text+0x114): undefined reference to 'default_huge_page_size'
> >>>>
> >>>> According to the latest selftests, 'default_huge_page_size' has been
> >>>> moved to 'vm_util.c'. So fix the error by the same way.
> >>>>
> >>>> Reviewed-by: Lance Yang <lance.yang@...ux.dev>
> >>>> Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
> >>>> ---
> >>>>  tools/testing/selftests/vm/Makefile      |  1 +
> >>>>  tools/testing/selftests/vm/userfaultfd.c | 24 ------------------------
> >>>>  tools/testing/selftests/vm/vm_util.c     | 21 +++++++++++++++++++++
> >>>>  tools/testing/selftests/vm/vm_util.h     |  1 +
> >>>>  4 files changed, 23 insertions(+), 24 deletions(-)
> >>>
> >>>
> >>> What commit id does this fix?  And again, why not just take the original
> >>
> >> Let me check which commit introduced the fix.
> >>
> >>> commits instead?
> >>
> >> I agree that taking the original commits would be preferable.
> >>
> >> However, it might involve quite a few patches to backport, which could
> >> be a bit of work.
> >
> > We can easily take lots of patches, don't worry about the quantity.  But
> > it would be good to figure out what caused this to break here, and not
> > in other branches.
> >
> 
> Hi Greg,
> 
> After checking with 'git blame map_hugetlb.c', the issue was introduced
> by commit a584c7734a4d (“selftests: mm: fix map_hugetlb failure on 64K
> page size systems”), which corresponds to upstream commit 91b80cc5b39f.
> This change appears to have caused the build error in the 6.1.y tree.
> 
> Comparing several stable trees shows the following:
> 
> - 6.0.y: not backported*
> - 6.1.y: backported
> - 6.2.y: not backported*
> - 6.3.y: not backported*
> - 6.4.y: not backported*
> - 6.5.y: not backported*
> - 6.6.y: backported
> - 6.7.y: backported
> 
> Given this, it might be preferable to revert a584c7734a4d in 6.1.y for
> consistency with the other stable trees (6.0.y, 6.2–6.5.y).

Ah, yeah, it looks like this commit was reverted from other stable
releases, as it shows up in the following releases:

	4.19.310 4.19.315 5.4.272 5.4.277 5.10.213 5.10.218 5.15.152 5.15.160 6.1.82 6.6.18 6.7.6

So a revert would be fine, want to submit it?

thanks,

greg k-h