[PATCH 08/28] locking/lockdep: Define INITIAL_CHAIN_KEY for chain keys to start with

[Yuyang Du <duyuyang@gmail.com>]

Chain keys are computed using Jenkins hash function, which needs an initial
hash to start with. Dedicate a macro to make this clear and configurable. A
later patch changes this initial chain key.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 include/linux/lockdep.h  |  1 +
 init/init_task.c         |  2 +-
 kernel/locking/lockdep.c | 18 +++++++++---------
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 751a2cc..bb47d7c 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -229,6 +229,7 @@ struct lock_chain {
  * bitfield and hitting the BUG in hlock_class().
  */
 #define MAX_LOCKDEP_KEYS		((1UL << MAX_LOCKDEP_KEYS_BITS) - 1)
+#define INITIAL_CHAIN_KEY		0
 
 struct held_lock {
 	/*
diff --git a/init/init_task.c b/init/init_task.c
index 1b15cb9..afa6ad7 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -167,7 +167,7 @@ struct task_struct init_task
 #endif
 #ifdef CONFIG_LOCKDEP
 	.lockdep_depth = 0, /* no locks held yet */
-	.curr_chain_key = 0,
+	.curr_chain_key = INITIAL_CHAIN_KEY,
 	.lockdep_recursion = 0,
 #endif
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4ce0e39..3055ea7 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -361,7 +361,7 @@ static inline u64 iterate_chain_key(u64 key, u32 idx)
 inline void lockdep_init_task(struct task_struct *task)
 {
 	task->lockdep_depth = 0; /* no locks held yet */
-	task->curr_chain_key = 0;
+	task->curr_chain_key = INITIAL_CHAIN_KEY;
 	task->lockdep_recursion = 0;
 }
 
@@ -852,7 +852,7 @@ static bool class_lock_list_valid(struct lock_class *c, struct list_head *h)
 static bool check_lock_chain_key(struct lock_chain *chain)
 {
 #ifdef CONFIG_PROVE_LOCKING
-	u64 chain_key = 0;
+	u64 chain_key = INITIAL_CHAIN_KEY;
 	int i;
 
 	for (i = chain->base; i < chain->base + chain->depth; i++)
@@ -2414,7 +2414,7 @@ static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
 print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_next)
 {
 	struct held_lock *hlock;
-	u64 chain_key = 0;
+	u64 chain_key = INITIAL_CHAIN_KEY;
 	int depth = curr->lockdep_depth;
 	int i = get_first_held_lock(curr, hlock_next);
 
@@ -2434,7 +2434,7 @@ static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
 static void print_chain_keys_chain(struct lock_chain *chain)
 {
 	int i;
-	u64 chain_key = 0;
+	u64 chain_key = INITIAL_CHAIN_KEY;
 	int class_id;
 
 	printk("depth: %u\n", chain->depth);
@@ -2742,7 +2742,7 @@ static void check_chain_key(struct task_struct *curr)
 #ifdef CONFIG_DEBUG_LOCKDEP
 	struct held_lock *hlock, *prev_hlock = NULL;
 	unsigned int i;
-	u64 chain_key = 0;
+	u64 chain_key = INITIAL_CHAIN_KEY;
 
 	for (i = 0; i < curr->lockdep_depth; i++) {
 		hlock = curr->held_locks + i;
@@ -2766,7 +2766,7 @@ static void check_chain_key(struct task_struct *curr)
 
 		if (prev_hlock && (prev_hlock->irq_context !=
 							hlock->irq_context))
-			chain_key = 0;
+			chain_key = INITIAL_CHAIN_KEY;
 		chain_key = iterate_chain_key(chain_key, hlock->class_idx);
 		prev_hlock = hlock;
 	}
@@ -3681,14 +3681,14 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		/*
 		 * How can we have a chain hash when we ain't got no keys?!
 		 */
-		if (DEBUG_LOCKS_WARN_ON(chain_key != 0))
+		if (DEBUG_LOCKS_WARN_ON(chain_key != INITIAL_CHAIN_KEY))
 			return 0;
 		chain_head = 1;
 	}
 
 	hlock->prev_chain_key = chain_key;
 	if (separate_irq_context(curr, hlock)) {
-		chain_key = 0;
+		chain_key = INITIAL_CHAIN_KEY;
 		chain_head = 1;
 	}
 	chain_key = iterate_chain_key(chain_key, class_idx);
@@ -4530,7 +4530,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
 	return;
 
 recalc:
-	chain_key = 0;
+	chain_key = INITIAL_CHAIN_KEY;
 	for (i = chain->base; i < chain->base + chain->depth; i++)
 		chain_key = iterate_chain_key(chain_key, chain_hlocks[i] + 1);
 	if (chain->depth && chain->chain_key == chain_key)
-- 
1.8.3.1