The patch titled
Subject: mm: avoid VM_BUG_ON when try to map an anon large folio to zero page.
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-avoid-vm_bug_on-when-try-to-map-an-anon-large-folio-to-zero-page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-avoid-vm_bug_on-when-try-to-map-an-anon-large-folio-to-zero-page.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
Subject: mm: avoid VM_BUG_ON when try to map an anon large folio to zero page.
Date: Wed, 23 Oct 2024 13:12:36 -0400
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.
Link: https://lkml.kernel.org/r/20241023171236.1122535-1-ziy@xxxxxxxxxx
Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: kernel-team@xxxxxxxx
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Cc: Nico Pache <npache@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Usama Arif <usamaarif642@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/migrate.c~mm-avoid-vm_bug_on-when-try-to-map-an-anon-large-folio-to-zero-page
+++ a/mm/migrate.c
@@ -206,7 +206,8 @@ static bool try_to_map_unused_to_zeropag
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);
_
Patches currently in -mm which might be from ziy@xxxxxxxxxx are
mm-avoid-vm_bug_on-when-try-to-map-an-anon-large-folio-to-zero-page.patch
mm-avoid-zeroing-user-movable-page-twice-with-init_on_alloc=1.patch
