This will be used to support mshare functionality where the read
lock on an mshare host mm is taken while holding the lock on a
process mm.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 include/linux/mmap_lock.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 2c9fffa58714..3cf7219306a1 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -369,6 +369,13 @@ static inline void mmap_read_lock(struct mm_struct *mm)
 	__mmap_lock_trace_acquire_returned(mm, false, true);
 }
 
+static inline void mmap_read_lock_nested(struct mm_struct *mm, int subclass)
+{
+	__mmap_lock_trace_start_locking(mm, false);
+	down_read_nested(&mm->mmap_lock, subclass);
+	__mmap_lock_trace_acquire_returned(mm, false, true);
+}
+
 static inline int mmap_read_lock_killable(struct mm_struct *mm)
 {
 	int ret;
-- 
2.47.1