Re: [PATCH] mm: avoid VM_BUG_ON when try to map an anon large folio to zero page.

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On 23.10.24 19:12, Zi Yan wrote:
An anonymous large folio can be split into non order-0 folios,
try_to_map_unused_to_zeropage() should not VM_BUG_ON compound pages but
just return false. This fixes the crash when splitting anonymous large
folios to non order-0 folios.

Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
  mm/migrate.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index e950fd62607f..7ffdbe078aa7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -206,7 +206,8 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
  	pte_t newpte;
  	void *addr;
- VM_BUG_ON_PAGE(PageCompound(page), page);
+	if (PageCompound(page))
+		return false;
  	VM_BUG_ON_PAGE(!PageAnon(page), page);
  	VM_BUG_ON_PAGE(!PageLocked(page), page);
  	VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page);

Would read nicer in 2024 when working on folios ;)

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb





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