[merged mm-stable] mm-huge_memory-handle-buggy-pmd-entry-in-zap_huge_pmd.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: mm/huge_memory: handle buggy PMD entry in zap_huge_pmd()
has been removed from the -mm tree.  Its filename was
     mm-huge_memory-handle-buggy-pmd-entry-in-zap_huge_pmd.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Lorenzo Stoakes (Oracle)" <ljs@kernel.org>
Subject: mm/huge_memory: handle buggy PMD entry in zap_huge_pmd()
Date: Fri, 20 Mar 2026 18:07:21 +0000

A recent bug I analysed managed to, through a bug in the userfaultfd
implementation, reach an invalid point in the zap_huge_pmd() code where
the PMD was none of:

- A non-DAX, PFN or mixed map.
- The huge zero folio
- A present PMD entry
- A softleaf entry

The code at this point calls folio_test_anon() on a known-NULL folio.
Having logic like this explicitly NULL dereference in the code is hard to
understand, and makes debugging potentially more difficult.

Add an else branch to handle this case and WARN().

No functional change intended.

Link: https://lore.kernel.org/all/6b3d7ad7-49e1-407a-903d-3103704160d8@lucifer.local/
Link: https://lkml.kernel.org/r/fcf1f6de84a2ace188b6bf103fa15dde695f1ed8.1774029655.git.ljs@kernel.org
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/huge_memory.c~mm-huge_memory-handle-buggy-pmd-entry-in-zap_huge_pmd
+++ a/mm/huge_memory.c
@@ -2462,6 +2462,10 @@ bool zap_huge_pmd(struct mmu_gather *tlb
 
 		if (!thp_migration_supported())
 			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+	} else {
+		WARN_ON_ONCE(true);
+		spin_unlock(ptl);
+		return true;
 	}
 
 	if (folio_test_anon(folio)) {
_

Patches currently in -mm which might be from ljs@kernel.org are

maintainers-update-mglru-entry-to-reflect-current-status.patch
selftests-mm-add-merge-test-for-partial-msealed-range.patch