[PATCH v4 20/30] locking/lockdep: Update direct dependency's read-write type if it exists

[Yuyang Du <duyuyang@gmail.com>]

When adding a dependency, if the dependency exists the dependency's
read-write type will be "upgraded" if the new dependency has more
exclusive lock types. The order toward more exclusiveness is:

    recursive read -> read -> write.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 kernel/locking/lockdep.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 41cb735..eb88314 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1588,6 +1588,21 @@ static inline int get_lock_type2(struct lock_list *lock)
 	return lock->lock_type2;
 }
 
+static inline int hlock_type(struct held_lock *hlock)
+{
+	return hlock->read;
+}
+
+static inline void set_lock_type1(struct lock_list *lock, int read)
+{
+	lock->lock_type1 = read;
+}
+
+static inline void set_lock_type2(struct lock_list *lock, int read)
+{
+	lock->lock_type2 = read;
+}
+
 /*
  * Forward- or backward-dependency search, used for both circular dependency
  * checking and hardirq-unsafe/softirq-unsafe checking.
@@ -2585,6 +2600,17 @@ static inline void inc_chains(void)
 			list_add_tail_rcu(&chain->chain_entry, &entry->chains);
 			__set_bit(chain - lock_chains, lock_chains_in_dep);
 
+			/*
+			 * For a direct dependency, smaller type value
+			 * generally means more lock exlusiveness; we
+			 * keep the more exlusive one, in other words,
+			 * we "upgrade" the dependency if we can.
+			 */
+			if (prev->read < get_lock_type1(entry))
+				set_lock_type1(entry, prev->read);
+			if (next->read < get_lock_type2(entry))
+				set_lock_type2(entry, next->read);
+
 			if (distance == 1)
 				entry->distance = 1;
 
-- 
1.8.3.1