[PATCH 1/2] mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE
From: Andrea Arcangeli <hidden>
Date: 2016-09-15 17:41:48
Subsystem:
memory management, memory management - memory policy and migration, memory management - thp (transparent huge page), memory mapping, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett, Linus Torvalds
vma->vm_page_prot is read lockless from the rmap_walk, it may be updated concurrently and this prevents the risk of reading intermediate values. Signed-off-by: Andrea Arcangeli <redacted> --- mm/huge_memory.c | 2 +- mm/migrate.c | 2 +- mm/mmap.c | 9 ++++++--- 3 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cb95a83..995f8a1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c@@ -1566,7 +1566,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, if (soft_dirty) entry = pte_swp_mksoft_dirty(entry); } else { - entry = mk_pte(page + i, vma->vm_page_prot); + entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot)); entry = maybe_mkwrite(entry, vma); if (!write) entry = pte_wrprotect(entry);
diff --git a/mm/migrate.c b/mm/migrate.c
index 00167df..e49ccce 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c@@ -234,7 +234,7 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma, goto unlock; get_page(new); - pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); + pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot))); if (pte_swp_soft_dirty(*ptep)) pte = pte_mksoft_dirty(pte);
diff --git a/mm/mmap.c b/mm/mmap.c
index c34f643..1abf106 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c@@ -112,13 +112,16 @@ static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags) void vma_set_page_prot(struct vm_area_struct *vma) { unsigned long vm_flags = vma->vm_flags; + pgprot_t vm_page_prot; - vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags); + vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags); if (vma_wants_writenotify(vma)) { vm_flags &= ~VM_SHARED; - vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, - vm_flags); + vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, + vm_flags); } + /* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */ + WRITE_ONCE(vma->vm_page_prot, vm_page_prot); } static unsigned long vm_mergeable __read_mostly; --
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