vm_flags are among VMA attributes which affect decisions like VMA merging
and splitting. Therefore all vm_flags modifications are performed after
taking exclusive mmap_lock to prevent vm_flags updates racing with such
operations. Introduce modifier functions for vm_flags to be used whenever
flags are updated. This way we can better check and control correct
locking behavior during these updates.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/mm.h       | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/mm_types.h |  8 +++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c2f62bdce134..b71f2809caac 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -627,6 +627,43 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
 	INIT_LIST_HEAD(&vma->anon_vma_chain);
 }
 
+/* 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)

+{
+	vma->vm_flags = flags;
+}
+
+/* Use when VMA is part of the VMA tree and modifications need coordination */
+static inline void reset_vm_flags(struct vm_area_struct *vma,
+				  unsigned long flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	init_vm_flags(vma, flags);
+}
+
+static inline void set_vm_flags(struct vm_area_struct *vma,
+				unsigned long flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	vma->vm_flags |= flags;
+}
+
+static inline void clear_vm_flags(struct vm_area_struct *vma,
+				  unsigned long flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	vma->vm_flags &= ~flags;
+}
+
+static inline void mod_vm_flags(struct vm_area_struct *vma,
+				unsigned long set, unsigned long clear)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	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 2d6d790d9bed..6c7c70bf50dd 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h

@@ -491,7 +491,13 @@ 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.
+	 * Use {init|reset|set|clear|mod}_vm_flags() functions instead.
+	 */
+	unsigned long vm_flags;
 
 	/*
 	 * For areas with an address space and backing store,

-- 
2.39.1