lockdep: Make lockdep checking constant

There are several places in the kernel which would like to pass a const
pointer to lockdep_is_held().  Constify the entire path so nobody has to
trick the compiler.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "David S. Miller" <davem@davemloft.net>
Link: https://lkml.kernel.org/r/20180117151414.23686-3-willy@infradead.org

include/linux/lockdep.h

@@ -337,9 +337,9 @@ extern void lock_release(struct lockdep_map *lock, int nested,
 /*
  * Same "read" as for lock_acquire(), except -1 means any.
  */
-extern int lock_is_held_type(struct lockdep_map *lock, int read);
+extern int lock_is_held_type(const struct lockdep_map *lock, int read);
 
-static inline int lock_is_held(struct lockdep_map *lock)
+static inline int lock_is_held(const struct lockdep_map *lock)
 {
 	return lock_is_held_type(lock, -1);
 }

kernel/locking/lockdep.c

@@ -648,7 +648,7 @@ static int count_matching_names(struct lock_class *new_class)
 }
 
 static inline struct lock_class *
-look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
+look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
 {
 	struct lockdep_subclass_key *key;
 	struct hlist_head *hash_head;
@@ -3276,7 +3276,7 @@ print_lock_nested_lock_not_held(struct task_struct *curr,
 	return 0;
 }
 
-static int __lock_is_held(struct lockdep_map *lock, int read);
+static int __lock_is_held(const struct lockdep_map *lock, int read);
 
 /*
  * This gets called for every mutex_lock*()/spin_lock*() operation.
@@ -3485,13 +3485,14 @@ print_unlock_imbalance_bug(struct task_struct *curr, struct lockdep_map *lock,
 	return 0;
 }
 
-static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
+static int match_held_lock(const struct held_lock *hlock,
+					const struct lockdep_map *lock)
 {
 	if (hlock->instance == lock)
 		return 1;
 
 	if (hlock->references) {
-		struct lock_class *class = lock->class_cache[0];
+		const struct lock_class *class = lock->class_cache[0];
 
 		if (!class)
 			class = look_up_lock_class(lock, 0);
@@ -3727,7 +3728,7 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 	return 1;
 }
 
-static int __lock_is_held(struct lockdep_map *lock, int read)
+static int __lock_is_held(const struct lockdep_map *lock, int read)
 {
 	struct task_struct *curr = current;
 	int i;
@@ -3941,7 +3942,7 @@ void lock_release(struct lockdep_map *lock, int nested,
 }
 EXPORT_SYMBOL_GPL(lock_release);
 
-int lock_is_held_type(struct lockdep_map *lock, int read)
+int lock_is_held_type(const struct lockdep_map *lock, int read)
 {
 	unsigned long flags;
 	int ret = 0;