[PATCH 13/41] mm: introduce vma->vm_flags modifier functions

[Suren Baghdasaryan]

To keep vma locking correctness when vm_flags are modified, add modifier
functions to be used whenever flags are updated.

Signed-off-by: Suren Baghdasaryan <surenb at google.com>
---
 include/linux/mm.h       | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/mm_types.h |  8 +++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ec2c4c227d51..35cf0a6cbcc2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -702,6 +702,44 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
 	vma_init_lock(vma);
 }
 
+/* Use when VMA is not part of the VMA tree and needs no locking */
+static inline
+void init_vm_flags(struct vm_area_struct *vma, unsigned long flags)
+{
+	WRITE_ONCE(vma->vm_flags, flags);
+}
+
+/* Use when VMA is part of the VMA tree and needs appropriate locking */
+static inline
+void reset_vm_flags(struct vm_area_struct *vma, unsigned long flags)
+{
+	vma_write_lock(vma);
+	init_vm_flags(vma, flags);
+}
+
+static inline
+void set_vm_flags(struct vm_area_struct *vma, unsigned long flags)
+{
+	vma_write_lock(vma);
+	vma->vm_flags |= flags;
+}
+
+static inline
+void clear_vm_flags(struct vm_area_struct *vma, unsigned long flags)
+{
+	vma_write_lock(vma);
+	vma->vm_flags &= ~flags;
+}
+
+static inline
+void mod_vm_flags(struct vm_area_struct *vma,
+		  unsigned long set, unsigned long clear)
+{
+	vma_write_lock(vma);
+	vma->vm_flags |= set;
+	vma->vm_flags &= ~clear;
+}
+
 static inline void vma_set_anonymous(struct vm_area_struct *vma)
 {
 	vma->vm_ops = NULL;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5f7c5ca89931..0d27edd3e63a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -553,7 +553,13 @@ struct vm_area_struct {
 	 * See vmf_insert_mixed_prot() for discussion.
 	 */
 	pgprot_t vm_page_prot;
-	unsigned long vm_flags;		/* Flags, see mm.h. */
+
+	/*
+	 * Flags, see mm.h.
+	 * WARNING! Do not modify directly to keep correct VMA locking.
+	 * Use {init|reset|set|clear|mod}_vm_flags() functions instead.
+	 */
+	unsigned long vm_flags;
 
 #ifdef CONFIG_PER_VMA_LOCK
 	int vm_lock_seq;
-- 
2.39.0