Re: [PATCH] mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Mar 19, 2026 at 8:14 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 19 Mar 2026 16:31:53 +0800 Hao Ge <hao.ge@linux.dev> wrote:
>
> > Due to initialization ordering, page_ext is allocated and initialized
> > relatively late during boot. Some pages have already been allocated
> > and freed before page_ext becomes available, leaving their codetag
> > uninitialized.
> >
> > A clear example is in init_section_page_ext(): alloc_page_ext() calls
> > kmemleak_alloc(). If the slab cache has no free objects, it falls back
> > to the buddy allocator to allocate memory. However, at this point page_ext
> > is not yet fully initialized, so these newly allocated pages have no
> > codetag set. These pages may later be reclaimed by KASAN,which causes
> > the warning to trigger when they are freed because their codetag ref is
> > still empty.
> >
> > Use a global array to track pages allocated before page_ext is fully
> > initialized, similar to how kmemleak tracks early allocations.
> > When page_ext initialization completes, set their codetag
> > to empty to avoid warnings when they are freed later.
>
> AI review asks questions:
>         https://sashiko.dev/#/patchset/20260319083153.2488005-1-hao.ge%40linux.dev

Impressive!