[PATCH v4 22/30] locking/lockdep: Hash held lock's read-write type into chain key

[Yuyang Du]

When computing a chain's hash key, we need to consider a held lock's
read-write type. To do so, we hash the held lock's read-write type into the
chain key. So the additional data to use Jenkins hash algorithm is a
composite of the new held lock's lock class index (lower 16 bits) and its
read-write type (higher 16 bits) as opposed to just class index before:

        held lock type (16 bits) : lock class index (16 bits)

Signed-off-by: Yuyang Du <duyuyang@xxxxxxxxx>
---
 include/linux/lockdep.h  |  1 +
 kernel/locking/lockdep.c | 55 ++++++++++++++++++++++++++++++++++--------------
 2 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index eab8a90..3de4b37 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -183,6 +183,7 @@ static inline void lockdep_copy_map(struct lockdep_map *to,
 }
 
 #define LOCK_TYPE_BITS	2
+#define LOCK_TYPE_SHIFT	16
 
 /*
  * Every lock has a list of other locks that were taken after or before
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1166262..d13b6b7 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -370,11 +370,22 @@ struct pending_free {
  * it's a hash of all locks taken up to that lock, including that lock.
  * It's a 64-bit hash, because it's important for the keys to be
  * unique.
+ *
+ * The additional u32 data to hash is a composite of the new held lock's
+ * lock class index (lower 16 bits) and its read-write type (higher 16
+ * bits):
+ *
+ *     hlock type (16 bits) : lock class index (16 bits)
+ *
+ * N.B. The bits taken for lock type and index are specified by
+ * LOCK_TYPE_SHIFT.
  */
-static inline u64 iterate_chain_key(u64 key, u32 idx)
+static inline u64 iterate_chain_key(u64 key, u32 idx, int hlock_type)
 {
 	u32 k0 = key, k1 = key >> 32;
 
+	idx += hlock_type << LOCK_TYPE_SHIFT;
+
 	__jhash_mix(idx, k0, k1); /* Macro that modifies arguments! */
 
 	return k0 | (u64)k1 << 32;
@@ -960,7 +971,8 @@ static bool check_lock_chain_key(struct lock_chain *chain)
 	int i;
 
 	for (i = chain->base; i < chain->base + chain->depth; i++)
-		chain_key = iterate_chain_key(chain_key, chain_hlocks[i]);
+		chain_key = iterate_chain_key(chain_key, chain_hlocks[i],
+					      chain_hlocks_type[i]);
 	/*
 	 * The 'unsigned long long' casts avoid that a compiler warning
 	 * is reported when building tools/lib/lockdep.
@@ -2700,12 +2712,13 @@ static inline int get_first_held_lock(struct task_struct *curr,
 /*
  * Returns the next chain_key iteration
  */
-static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
+static u64 print_chain_key_iteration(int class_idx, u64 chain_key, int lock_type)
 {
-	u64 new_chain_key = iterate_chain_key(chain_key, class_idx);
+	u64 new_chain_key = iterate_chain_key(chain_key, class_idx, lock_type);
 
-	printk(" class_idx:%d -> chain_key:%016Lx",
+	printk(" class_idx:%d (lock_type %d) -> chain_key:%016Lx",
 		class_idx,
+		lock_type,
 		(unsigned long long)new_chain_key);
 	return new_chain_key;
 }
@@ -2722,12 +2735,15 @@ static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
 		hlock_next->irq_context);
 	for (; i < depth; i++) {
 		hlock = curr->held_locks + i;
-		chain_key = print_chain_key_iteration(hlock->class_idx, chain_key);
+		chain_key = print_chain_key_iteration(hlock->class_idx,
+						      chain_key,
+						      hlock->read);
 
 		print_lock(hlock);
 	}
 
-	print_chain_key_iteration(hlock_next->class_idx, chain_key);
+	print_chain_key_iteration(hlock_next->class_idx, chain_key,
+				  hlock_next->read);
 	print_lock(hlock_next);
 }
 
@@ -2735,12 +2751,14 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 {
 	int i;
 	u64 chain_key = INITIAL_CHAIN_KEY;
-	int class_id;
+	int class_id, lock_type;
 
 	printk("depth: %u\n", chain->depth);
 	for (i = 0; i < chain->depth; i++) {
 		class_id = chain_hlocks[chain->base + i];
-		chain_key = print_chain_key_iteration(class_id, chain_key);
+		lock_type = chain_hlocks_type[chain->base + i];
+		chain_key = print_chain_key_iteration(class_id, chain_key,
+						      lock_type);
 
 		print_lock_name(lock_classes + class_id);
 		printk("\n");
@@ -2780,7 +2798,7 @@ static int check_no_collision(struct task_struct *curr, struct held_lock *hlock,
 			      struct lock_chain *chain, int depth)
 {
 #ifdef CONFIG_DEBUG_LOCKDEP
-	int i, j, id;
+	int i, j, id, type;
 
 	i = get_first_held_lock(curr, hlock, depth);
 
@@ -2789,10 +2807,12 @@ static int check_no_collision(struct task_struct *curr, struct held_lock *hlock,
 		return 0;
 	}
 
-	for (j = 0; j < chain->depth - 1; j++, i++) {
+	for (j = chain->base; j < chain->base + chain->depth - 1; j++, i++) {
 		id = curr->held_locks[i].class_idx;
+		type = curr->held_locks[i].read;
 
-		if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
+		if (DEBUG_LOCKS_WARN_ON((chain_hlocks[j] != id) ||
+					(chain_hlocks_type[j] != type))) {
 			print_collision(curr, hlock, chain, depth);
 			return 0;
 		}
@@ -3081,7 +3101,8 @@ static int validate_chain(struct task_struct *curr, struct held_lock *next,
 	 * lock_chains. If it exists the check is actually not needed.
 	 */
 	chain_key = iterate_chain_key(hlock->prev_chain_key,
-				      hlock_class(next) - lock_classes);
+				      hlock_class(next) - lock_classes,
+				      next->read);
 
 	goto chain_again;
 
@@ -3139,7 +3160,8 @@ static void check_chain_key(struct task_struct *curr)
 		if (prev_hlock && (prev_hlock->irq_context !=
 							hlock->irq_context))
 			chain_key = INITIAL_CHAIN_KEY;
-		chain_key = iterate_chain_key(chain_key, hlock->class_idx);
+		chain_key = iterate_chain_key(chain_key, hlock->class_idx,
+					      hlock->read);
 		prev_hlock = hlock;
 	}
 	if (chain_key != curr->curr_chain_key) {
@@ -4048,7 +4070,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	if (separate_irq_context(curr, hlock))
 		chain_key = INITIAL_CHAIN_KEY;
 
-	chain_key = iterate_chain_key(chain_key, class_idx);
+	chain_key = iterate_chain_key(chain_key, class_idx, read);
 
 	if (nest_lock && !__lock_is_held(nest_lock, -1)) {
 		print_lock_nested_lock_not_held(curr, hlock, ip);
@@ -4908,7 +4930,8 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
 recalc:
 	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]);
+		chain_key = iterate_chain_key(chain_key, chain_hlocks[i],
+					      chain_hlocks_type[i]);
 	if (chain->depth && chain->chain_key == chain_key)
 		return;
 	/* Overwrite the chain key for concurrent RCU readers. */
-- 
1.8.3.1