On Tue, Apr 21, 2026 at 10:20:41AM +0800, Muchun Song wrote:
> In section_activate(), if populate_section_memmap() fails, the error
> handling path calls section_deactivate() to roll back the state. This
> causes a vmemmap accounting imbalance.
>
> Since commit c3576889d87b ("mm: fix accounting of memmap pages"),
> memmap pages are accounted for only after populate_section_memmap()
> succeeds. However, the failure path unconditionally calls
> section_deactivate(), which decreases the vmemmap count. Consequently,
> a failure in populate_section_memmap() leads to an accounting underflow,
> incorrectly reducing the system's tracked vmemmap usage.
>
> Fix this more thoroughly by moving all accounting calls into the lower
> level functions that actually perform the vmemmap allocation and freeing:
>
> - populate_section_memmap() accounts for newly allocated vmemmap pages
> - depopulate_section_memmap() unaccounts when vmemmap is freed
>
> This ensures proper accounting in all code paths, including error
> handling and early section cases.
>
> Fixes: c3576889d87b ("mm: fix accounting of memmap pages")
> Signed-off-by: Muchun Song <[email protected]>
> Acked-by: Mike Rapoport (Microsoft) <[email protected]>
Acked-by: Oscar Salvador <[email protected]>
--
Oscar Salvador
SUSE Labs
