[PATCH 1/2] mm/vma: add vma_is_*_locked() helpers

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Add vma_is_read_locked(), vma_is_write_locked() and vma_is_locked() helpers
and utilise them in vma_assert_locked() and vma_assert_write_locked().

These functions will intentionally not be defined if CONFIG_PER_VMA_LOCK is
not set, as they would not make any sense in a context where VMA locks do
not exist.

This lays the groundwork for a subsequent change that allows for asserting
that either the mmap lock or VMA lock is held.

Suggested-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 include/linux/mmap_lock.h | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index b50416fbba20..cd51e0a43c76 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -236,19 +236,31 @@ int vma_start_write_killable(struct vm_area_struct *vma)
 	return __vma_start_write(vma, mm_lock_seq, TASK_KILLABLE);
 }
 
-static inline void vma_assert_write_locked(struct vm_area_struct *vma)
+static inline bool vma_is_read_locked(struct vm_area_struct *vma)
+{
+	return refcount_read(&vma->vm_refcnt) > 1;
+}
+
+static inline bool vma_is_write_locked(struct vm_area_struct *vma)
 {
 	unsigned int mm_lock_seq;
 
-	VM_BUG_ON_VMA(!__is_vma_write_locked(vma, &mm_lock_seq), vma);
+	return __is_vma_write_locked(vma, &mm_lock_seq);
 }
 
-static inline void vma_assert_locked(struct vm_area_struct *vma)
+static inline bool vma_is_locked(struct vm_area_struct *vma)
 {
-	unsigned int mm_lock_seq;
+	return vma_is_read_locked(vma) || vma_is_write_locked(vma);
+}
 
-	VM_BUG_ON_VMA(refcount_read(&vma->vm_refcnt) <= 1 &&
-		      !__is_vma_write_locked(vma, &mm_lock_seq), vma);
+static inline void vma_assert_write_locked(struct vm_area_struct *vma)
+{
+	VM_BUG_ON_VMA(!vma_is_write_locked(vma), vma);
+}
+
+static inline void vma_assert_locked(struct vm_area_struct *vma)
+{
+	VM_BUG_ON_VMA(!vma_is_locked(vma), vma);
 }
 
 static inline bool vma_is_attached(struct vm_area_struct *vma)
-- 
2.52.0