Messages in this thread Patch in this message | | | Date | Wed, 9 Jun 2021 23:38:11 -0700 (PDT) | From | Hugh Dickins <> | Subject | [PATCH 03/11] mm: page_vma_mapped_walk(): use pmd_read_atomic() |
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page_vma_mapped_walk() cleanup: use pmd_read_atomic() with barrier() instead of READ_ONCE() for pmde: some architectures (e.g. i386 with PAE) have a multi-word pmd entry, for which READ_ONCE() is not good enough.
Signed-off-by: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> --- mm/page_vma_mapped.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index 7c0504641fb8..973c3c4e72cc 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -182,13 +182,16 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) pud = pud_offset(p4d, pvmw->address); if (!pud_present(*pud)) return false; + pvmw->pmd = pmd_offset(pud, pvmw->address); /* * Make sure the pmd value isn't cached in a register by the * compiler and used as a stale value after we've observed a * subsequent update. */ - pmde = READ_ONCE(*pvmw->pmd); + pmde = pmd_read_atomic(pvmw->pmd); + barrier(); + if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) { pvmw->ptl = pmd_lock(mm, pvmw->pmd); if (likely(pmd_trans_huge(*pvmw->pmd))) { -- 2.26.2
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