[PATCH v2 02/17] locking/lockdep: Add read-write type for dependency

[Yuyang Du]

Direct dependency needs to keep track of its locks' read-write types. A
union field is added to lock_list struct so the type is stored there as
this:

	lock_type[1] (u16), lock_type[0] (u16)

			or:

	dep_type (int)

where value:

 0: exclusive / write
 1: read
 2: recursive read

Note that (int) dep_type value may vary with different architectural
endianness, so use helper functions to operate on these types.

Signed-off-by: Yuyang Du <duyuyang@xxxxxxxxx>
---
 include/linux/lockdep.h            | 12 ++++++++++++
 kernel/locking/lockdep.c           | 34 +++++++++++++++++++++++++++++++---
 kernel/locking/lockdep_internals.h |  3 +++
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1009c47..bc09c85 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -195,6 +195,18 @@ struct lock_list {
 	struct lock_class		*links_to;
 	struct lock_trace		trace;
 	int				distance;
+	/*
+	 * This field keeps track of the read-write type of this dependency.
+	 *
+	 * With L1 -> L2:
+	 *
+	 * lock_type[0] stores the type of L1, while lock_type[1] stores the
+	 * type of L2.
+	 */
+	union {
+		int	dep_type;
+		u16	lock_type[2];
+	};
 
 	/*
 	 * The parent field is used to implement breadth-first search, and the
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index fb6be63..e7eedbf 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1225,7 +1225,7 @@ static struct lock_list *alloc_list_entry(void)
 static int add_lock_to_list(struct lock_class *this,
 			    struct lock_class *links_to, struct list_head *head,
 			    unsigned long ip, int distance,
-			    struct lock_trace *trace)
+			    struct lock_trace *trace, int dep_type)
 {
 	struct lock_list *entry;
 	/*
@@ -1240,6 +1240,8 @@ static int add_lock_to_list(struct lock_class *this,
 	entry->links_to = links_to;
 	entry->distance = distance;
 	entry->trace = *trace;
+	entry->dep_type = dep_type;
+
 	/*
 	 * Both allocation and removal are done under the graph lock; but
 	 * iteration is under RCU-sched; see look_up_lock_class() and
@@ -1677,6 +1679,30 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 	return ret;
 }
 
+static inline int get_dep_type(struct held_lock *lock1, struct held_lock *lock2)
+{
+	/*
+	 * With dependency lock1 -> lock2:
+	 *
+	 * lock_type[0] is lock1, while lock_type[1] is lock2.
+	 *
+	 * Avoid architectural endianness difference composing dep_type.
+	 */
+	u16 type[2] = { lock1->read, lock2->read };
+
+	return *(int *)type;
+}
+
+static inline int get_lock_type1(struct lock_list *lock)
+{
+	return lock->lock_type[0];
+}
+
+static inline int get_lock_type2(struct lock_list *lock)
+{
+	return lock->lock_type[1];
+}
+
 /*
  * Check that the dependency graph starting at <src> can lead to
  * <target> or not. Print an error and return 0 if it does.
@@ -2446,14 +2472,16 @@ static inline void inc_chains(void)
 	 */
 	ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
 			       &hlock_class(prev)->locks_after,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance, trace,
+			       get_dep_type(prev, next));
 
 	if (!ret)
 		return 0;
 
 	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
 			       &hlock_class(next)->locks_before,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance, trace,
+			       get_dep_type(next, prev));
 	if (!ret)
 		return 0;
 
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 150ec3f..c287bcb 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -26,6 +26,9 @@ enum lock_usage_bit {
 #define LOCK_USAGE_DIR_MASK  2
 #define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK))
 
+#define LOCK_TYPE_BITS	16
+#define LOCK_TYPE_MASK	0xFFFF
+
 /*
  * Usage-state bitmasks:
  */
-- 
1.8.3.1