Re: [syzbot] [mm?] WARNING in page_add_anon_rmap

David Hildenbrand
2023-09-18T12:55:14Z

On 18.09.23 14:32, Matthew Wilcox wrote:
> On Mon, Sep 18, 2023 at 12:00:24PM +0200, David Hildenbrand wrote:
>>> If you want syzbot to run the reproducer, reply with:
>>> #syz test: git://repo/address.git branch-or-commit-hash
>>> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If I understand correctly, you have to do it like this:
>
> #syz test
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 789a2beb8b3a..f13a2927163d 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1249,8 +1249,10 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
> }
> if (flags & RMAP_EXCLUSIVE)
> SetPageAnonExclusive(page);
> - VM_WARN_ON_FOLIO(page_mapcount(page) > 1 && PageAnonExclusive(page),
> - folio);
> + /* While PTE-mapping a THP we have a PMD and a PTE mapping. */
> + VM_WARN_ON_FOLIO((atomic_read(&page->_mapcount) > 0 ||
> + (folio_test_large(folio) && folio_entire_mapcount(folio) > 1)) &&
> + PageAnonExclusive(page), folio);
> mlock_vma_folio(folio, vma, compound);
> }

Looks like an empty line went missing in your attempt.

Let's try again for fun (I reproduced and tested myself already ;) ).

#syz test

diff --git a/mm/rmap.c b/mm/rmap.c
index 789a2beb8b3a..f13a2927163d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1249,8 +1249,10 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
}
if (flags & RMAP_EXCLUSIVE)
SetPageAnonExclusive(page);
- VM_WARN_ON_FOLIO(page_mapcount(page) > 1 && PageAnonExclusive(page),
- folio);
+ /* While PTE-mapping a THP we have a PMD and a PTE mapping. */
+ VM_WARN_ON_FOLIO((atomic_read(&page->_mapcount) > 0 ||
+ (folio_test_large(folio) && folio_entire_mapcount(folio) > 1)) &&
+ PageAnonExclusive(page), folio);

mlock_vma_folio(folio, vma, compound);
}
--
2.41.0

--
Cheers,

David / dhildenb