[PATCH 1/8] mmap locking API: initial implementation as rwsem wrappers

[Michel Lespinasse <walken@google.com>]

This change wraps the existing mmap_sem related rwsem calls into a new
mmap locking API. There are two justifications for the new API:

- At first, it provides an easy hooking point to instrument mmap_sem
  locking latencies independently of any other rwsems.

- In the future, it may be a starting point for replacing the rwsem
  implementation with a different one, such as range locks.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
 include/linux/mm.h        |  1 +
 include/linux/mmap_lock.h | 59 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 include/linux/mmap_lock.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c54fb96cb1e6..2f13c9198999 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -15,6 +15,7 @@
 #include <linux/atomic.h>
 #include <linux/debug_locks.h>
 #include <linux/mm_types.h>
+#include <linux/mmap_lock.h>
 #include <linux/range.h>
 #include <linux/pfn.h>
 #include <linux/percpu-refcount.h>
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
new file mode 100644
index 000000000000..cffd25afe92b
--- /dev/null
+++ b/include/linux/mmap_lock.h
@@ -0,0 +1,59 @@
+#ifndef _LINUX_MMAP_LOCK_H
+#define _LINUX_MMAP_LOCK_H
+
+static inline void mmap_init_lock(struct mm_struct *mm)
+{
+	init_rwsem(&mm->mmap_sem);
+}
+
+static inline void mmap_write_lock(struct mm_struct *mm)
+{
+	down_write(&mm->mmap_sem);
+}
+
+static inline int mmap_write_lock_killable(struct mm_struct *mm)
+{
+	return down_write_killable(&mm->mmap_sem);
+}
+
+static inline bool mmap_write_trylock(struct mm_struct *mm)
+{
+	return down_write_trylock(&mm->mmap_sem) != 0;
+}
+
+static inline void mmap_write_unlock(struct mm_struct *mm)
+{
+	up_write(&mm->mmap_sem);
+}
+
+static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
+{
+	downgrade_write(&mm->mmap_sem);
+}
+
+static inline void mmap_read_lock(struct mm_struct *mm)
+{
+	down_read(&mm->mmap_sem);
+}
+
+static inline int mmap_read_lock_killable(struct mm_struct *mm)
+{
+	return down_read_killable(&mm->mmap_sem);
+}
+
+static inline bool mmap_read_trylock(struct mm_struct *mm)
+{
+	return down_read_trylock(&mm->mmap_sem) != 0;
+}
+
+static inline void mmap_read_unlock(struct mm_struct *mm)
+{
+	up_read(&mm->mmap_sem);
+}
+
+static inline bool mmap_is_locked(struct mm_struct *mm)
+{
+	return rwsem_is_locked(&mm->mmap_sem) != 0;
+}
+
+#endif /* _LINUX_MMAP_LOCK_H */
-- 
2.25.1.696.g5e7596f4ac-goog