[PATCH v4 18/30] ocking/lockdep: Add read-write type for a lock dependency

[Yuyang Du <duyuyang@gmail.com>]

Direct dependencies need to keep track of their read-write lock types.
Two bit fields, which share the distance field, are added to lock_list
struct to store the types.

With a dependecy lock1 -> lock2, lock_type1 has the type for lock1 and
lock_type2 has the type for lock2, where the values are one of the
lock_type enums.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 include/linux/lockdep.h  | 15 ++++++++++++++-
 kernel/locking/lockdep.c | 25 +++++++++++++++++++++++--
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 2335447..eab8a90 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -182,6 +182,8 @@ static inline void lockdep_copy_map(struct lockdep_map *to,
 		to->class_cache[i] = NULL;
 }
 
+#define LOCK_TYPE_BITS	2
+
 /*
  * Every lock has a list of other locks that were taken after or before
  * it as lock dependencies. These dependencies constitute a graph, which
@@ -204,7 +206,17 @@ struct lock_list {
 	struct list_head		chains;
 	struct lock_class		*class[2];
 	const struct lock_trace		*trace;
-	int				distance;
+
+	/*
+	 * The lock_type fields keep track of the lock type of this
+	 * dependency.
+	 *
+	 * With L1 -> L2, lock_type1 stores the lock type of L1, and
+	 * lock_type2 stores that of L2.
+	 */
+	unsigned int			lock_type1 : LOCK_TYPE_BITS,
+					lock_type2 : LOCK_TYPE_BITS,
+					distance   : 32 - 2*LOCK_TYPE_BITS;
 
 	/*
 	 * The parent field is used to implement breadth-first search.
@@ -359,6 +371,7 @@ enum lock_type {
 	LOCK_TYPE_WRITE		= 0,
 	LOCK_TYPE_READ,
 	LOCK_TYPE_RECURSIVE,
+	NR_LOCK_TYPE,
 };
 
 /*
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index bdc7e94..18303ff 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1379,9 +1379,17 @@ static int add_lock_to_list(struct lock_class *lock1,
 			    struct lock_class *lock2,
 			    unsigned long ip, int distance,
 			    const struct lock_trace *trace,
-			    struct lock_chain *chain)
+			    struct lock_chain *chain,
+			    int lock_type1, int lock_type2)
 {
 	struct lock_list *entry;
+
+	/*
+	 * The distance bit field in struct lock_list must be large
+	 * enough to hold the maximum lock depth.
+	 */
+	BUILD_BUG_ON((1 << (32 - 2*LOCK_TYPE_BITS)) < MAX_LOCK_DEPTH);
+
 	/*
 	 * Lock not present yet - get a new dependency struct and
 	 * add it to the list:
@@ -1394,6 +1402,8 @@ static int add_lock_to_list(struct lock_class *lock1,
 	entry->class[1] = lock2;
 	entry->distance = distance;
 	entry->trace = trace;
+	entry->lock_type1 = lock_type1;
+	entry->lock_type2 = lock_type2;
 
 	/*
 	 * Both allocation and removal are done under the graph lock; but
@@ -1537,6 +1547,16 @@ static inline struct list_head *get_dep_list(struct lock_list *lock, int forward
 	return &class->dep_list[forward];
 }
 
+static inline int get_lock_type1(struct lock_list *lock)
+{
+	return lock->lock_type1;
+}
+
+static inline int get_lock_type2(struct lock_list *lock)
+{
+	return lock->lock_type2;
+}
+
 /*
  * Forward- or backward-dependency search, used for both circular dependency
  * checking and hardirq-unsafe/softirq-unsafe checking.
@@ -2580,7 +2600,8 @@ static inline void inc_chains(void)
 	 * dependency list of the previous lock <prev>:
 	 */
 	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
-			       next->acquire_ip, distance, *trace, chain);
+			       next->acquire_ip, distance, *trace, chain,
+			       prev->read, next->read);
 	if (!ret)
 		return 0;
 
-- 
1.8.3.1