From 90888b4ae103e65e5dfd438adb8d7d7ece91afd2 Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes Date: Wed, 14 Jan 2026 11:56:19 +0000 Subject: [PATCH] mm: remove unnecessary and incorrect mmap lock assert This check was introduced by commit 42fc541404f2 ("mmap locking API: add mmap_assert_locked() and mmap_assert_write_locked()") which replaced a VM_BUG_ON_VMA() over rwsem_is_locked from commit a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages"), i.e. the commit that introduced PUD THPs. These seem to be careful asserts introduced to ensure that locks are held in general, however for a zap we require that VMAs are kept stable, and this is a requirement that has held perfectly well for a long time. These were long before VMA locks and thus there appears to be no reason to think this is assert is there for anything other than 'stabilised VMA'. Asserting that the VMA under examination is stable only in the case of a THP PUD is strange and unnecessary. If we wish to be careful and assert such things, we should do so at the zap level. However in any case the current situation is already simply incorrect - a VMA lock suffices here. Remove the assert for now as it is unnecessarily, incorrect and unhelpful, subsequent work can introduce an assert in general for zapping if required. Link: https://lkml.kernel.org/r/20260114115619.1087466-1-lorenzo.stoakes@oracle.com Fixes: 2ab7f1bbafc9 ("mm/madvise: allow guard page install/remove under VMA lock") Signed-off-by: Lorenzo Stoakes Reported-by: Chris Mason Closes: https://lore.kernel.org/all/20260113220856.2358195-1-clm@meta.com/ Acked-by: David Hildenbrand (Red Hat) Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: SeongJae Park Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/memory.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 2a55edc48a65..a0822b564cc0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1963,10 +1963,9 @@ static inline unsigned long zap_pud_range(struct mmu_gather *tlb, do { next = pud_addr_end(addr, end); if (pud_trans_huge(*pud)) { - if (next - addr != HPAGE_PUD_SIZE) { - mmap_assert_locked(tlb->mm); + if (next - addr != HPAGE_PUD_SIZE) split_huge_pud(vma, pud, addr); - } else if (zap_huge_pud(tlb, vma, pud, addr)) + else if (zap_huge_pud(tlb, vma, pud, addr)) goto next; /* fall through */ } -- 2.47.3