Re: [PATCH v2] mm/madvise: avoid skipping pages after splitting large folios

[Andrew Morton]

On Thu,  6 Aug 2026 13:55:01 +0800 Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx> wrote:

> madvise_inject_error() advances through the requested range using the
> size of the page returned by get_user_pages_fast(). Saving the size
> before error injection is required for hugetlb pages because successful
> soft offlining can dissolve the source huge page.
> 
> That stride is incorrect for non-hugetlb large folios in system memory.
> The memory failure handlers split such a folio and handle only the base
> page for the supplied PFN. Advancing by the pre-split folio size then
> skips the remaining pages in the requested range while madvise() still
> reports success.
> 
> Advance by PAGE_SIZE for non-hugetlb folios in system memory. Retain
> folio_size() for hugetlb and ZONE_DEVICE folios, as compound Device DAX
> folios are handled as a whole.

Thanks.

> Fixes: 19bfbe22f59a ("mm, hugetlb, soft_offline: save compound page order before page migration")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>

Should there be an Assisted-by: here?

When fixing a bug, please always describe the userspace-visible runtime
effects of that bug.  Especially when proposing a -stable backport.


I asked Gemini this question and then pasted in your email.  It told me
stuff, but I don't know if it's correct.  In this case it would be good
to hear that description in your own words, please.

And perhaps a means of reproducing the bug - clearly our selftests/
coverage here is poor.