[RFC PATCH 16/24] MM locking API: add vma locking API

[Michel Lespinasse <walken@google.com>]

This change adds the mm_vma_lock() and mm_vma_unlock() functions,
which are to be used to protect per-mm global structures (such as the
vma rbtree) when writers only hold a range lock.

The functions are no-ops when CONFIG_MM_LOCK_RANGE is not enabled,
as mmap_sem already protects such structures in that case.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
 include/linux/mm_lock.h  | 24 ++++++++++++++++++++----
 include/linux/mm_types.h |  2 ++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git include/linux/mm_lock.h include/linux/mm_lock.h
index a4d60bd56899..ebcc46bba211 100644
--- include/linux/mm_lock.h
+++ include/linux/mm_lock.h
@@ -14,6 +14,9 @@ static inline void mm_init_lock(struct mm_struct *mm)
        init_rwsem(&mm->mmap_sem);
 }
 
+static inline void mm_vma_lock(struct mm_struct *mm) {}
+static inline void mm_vma_unlock(struct mm_struct *mm) {}
+
 static inline void mm_init_coarse_lock_range(struct mm_lock_range *range) {}
 static inline void mm_init_lock_range(struct mm_lock_range *range,
 		unsigned long start, unsigned long end) {}
@@ -107,6 +110,9 @@ static inline void mm_init_lock(struct mm_struct *mm)
        init_rwsem(&mm->mmap_sem);
 }
 
+static inline void mm_vma_lock(struct mm_struct *mm) {}
+static inline void mm_vma_unlock(struct mm_struct *mm) {}
+
 static inline void mm_init_coarse_lock_range(struct mm_lock_range *range)
 {
 	range->mm = NULL;
@@ -131,10 +137,11 @@ static inline bool mm_range_is_coarse(struct mm_lock_range *range)
 #define __DEP_MAP_MM_LOCK_INITIALIZER(lockname)
 #endif
 
-#define MM_LOCK_INITIALIZER(name) {			\
-	.mutex = __MUTEX_INITIALIZER(name.mutex),	\
-	.rb_root = RB_ROOT,				\
-	__DEP_MAP_MM_LOCK_INITIALIZER(name)		\
+#define MM_LOCK_INITIALIZER(name) {				\
+	.mutex = __MUTEX_INITIALIZER(name.mutex),		\
+	.rb_root = RB_ROOT,					\
+	.vma_mutex = __MUTEX_INITIALIZER(name.vma_mutex),	\
+	__DEP_MAP_MM_LOCK_INITIALIZER(name)			\
 }
 
 #define MM_COARSE_LOCK_RANGE_INITIALIZER {		\
@@ -148,9 +155,18 @@ static inline void mm_init_lock(struct mm_struct *mm)
 
 	mutex_init(&mm->mmap_sem.mutex);
 	mm->mmap_sem.rb_root = RB_ROOT;
+	mutex_init(&mm->mmap_sem.vma_mutex);
 	lockdep_init_map(&mm->mmap_sem.dep_map, "&mm->mmap_sem", &__key, 0);
 }
 
+static inline void mm_vma_lock(struct mm_struct *mm) {
+	mutex_lock(&mm->mmap_sem.vma_mutex);
+}
+
+static inline void mm_vma_unlock(struct mm_struct *mm) {
+	mutex_unlock(&mm->mmap_sem.vma_mutex);
+}
+
 static inline void mm_init_lock_range(struct mm_lock_range *range,
 		unsigned long start, unsigned long end) {
 	range->start = start;
diff --git include/linux/mm_types.h include/linux/mm_types.h
index 941610c906b3..c40341d851cb 100644
--- include/linux/mm_types.h
+++ include/linux/mm_types.h
@@ -292,9 +292,11 @@ struct mm_lock {
 	struct mutex mutex;
 	struct rb_root rb_root;
 	unsigned long seq;
+	struct mutex vma_mutex;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif
+
 };
 #endif
 
-- 
2.25.0.341.g760bfbb309-goog