[PATCH v2 08/17] locking/lockdep: Add support for nestable terminal locks

[Waiman Long]

There are use cases where we want to allow nesting of one terminal lock
underneath another terminal-like lock. That new lock type is called
nestable terminal lock which can optionally allow the acquisition of
no more than one regular (non-nestable) terminal lock underneath it.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 include/linux/lockdep.h            |  9 ++++++++-
 kernel/locking/lockdep.c           | 15 +++++++++++++--
 kernel/locking/lockdep_internals.h |  2 +-
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index a146bca..b9435fb 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -148,16 +148,20 @@ struct lock_class_stats {
  * 1) LOCKDEP_FLAG_NOVALIDATE: No full validation, just simple checks.
  * 2) LOCKDEP_FLAG_TERMINAL: This is a terminal lock where lock/unlock on
  *    another lock within its critical section is not allowed.
+ * 3) LOCKDEP_FLAG_TERMINAL_NESTABLE: This is a terminal lock that can
+ *    allow one more regular terminal lock to be nested underneath it.
  *
  * Only the least significant 4 bits of the flags will be copied to the
  * held_lock structure.
  */
 #define LOCKDEP_FLAG_TERMINAL		(1 << 0)
+#define LOCKDEP_FLAG_TERMINAL_NESTABLE	(1 << 1)
 #define LOCKDEP_FLAG_NOVALIDATE 	(1 << 4)
 
 #define LOCKDEP_HLOCK_FLAGS_MASK	0x0f
 #define LOCKDEP_NOCHECK_FLAGS		(LOCKDEP_FLAG_NOVALIDATE |\
-					 LOCKDEP_FLAG_TERMINAL)
+					 LOCKDEP_FLAG_TERMINAL	 |\
+					 LOCKDEP_FLAG_TERMINAL_NESTABLE)
 
 /*
  * Map the lock object (the lock instance) to the lock-class object.
@@ -327,6 +331,8 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
 	do { (lock)->dep_map.flags |= LOCKDEP_FLAG_NOVALIDATE; } while (0)
 #define lockdep_set_terminal_class(lock) \
 	do { (lock)->dep_map.flags |= LOCKDEP_FLAG_TERMINAL; } while (0)
+#define lockdep_set_terminal_nestable_class(lock) \
+	do { (lock)->dep_map.flags |= LOCKDEP_FLAG_TERMINAL_NESTABLE; } while (0)
 
 /*
  * Compare locking classes
@@ -444,6 +450,7 @@ static inline void lockdep_on(void)
 
 #define lockdep_set_novalidate_class(lock)	do { } while (0)
 #define lockdep_set_terminal_class(lock)	do { } while (0)
+#define lockdep_set_terminal_nestable_class(lock)	do { } while (0)
 
 /*
  * We don't define lockdep_match_class() and lockdep_match_key() for !LOCKDEP
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 40894c1..5a853a6 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3263,13 +3263,24 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	class_idx = class - lock_classes + 1;
 
 	if (depth) {
+		int prev_type;
+
 		hlock = curr->held_locks + depth - 1;
 
 		/*
-		 * Warn if the previous lock is a terminal lock.
+		 * Warn if the previous lock is a terminal lock or the
+		 * previous lock is a nestable terminal lock and the current
+		 * one isn't a regular terminal lock.
 		 */
-		if (DEBUG_LOCKS_WARN_ON(hlock_is_terminal(hlock)))
+		prev_type = hlock_is_terminal(hlock);
+		if (DEBUG_LOCKS_WARN_ON((prev_type == LOCKDEP_FLAG_TERMINAL) ||
+			((prev_type == LOCKDEP_FLAG_TERMINAL_NESTABLE) &&
+			 (flags_is_terminal(class->flags) !=
+				LOCKDEP_FLAG_TERMINAL)))) {
+			pr_warn("Terminal lock error: prev lock = %s, curr lock = %s\n",
+				hlock->instance->name, class->name);
 			return 0;
+		}
 
 		if (hlock->class_idx == class_idx && nest_lock) {
 			if (hlock->references) {
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 271fba8..51fa141 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -215,5 +215,5 @@ static inline unsigned long debug_class_ops_read(struct lock_class *class)
 
 static inline unsigned int flags_is_terminal(unsigned int flags)
 {
-	return flags & LOCKDEP_FLAG_TERMINAL;
+	return flags & (LOCKDEP_FLAG_TERMINAL|LOCKDEP_FLAG_TERMINAL_NESTABLE);
 }
-- 
1.8.3.1