locking/lockdep: Add support for dynamic keys

A shortcoming of the current lockdep implementation is that it requires
lock keys to be allocated statically. That forces all instances of lock
objects that occur in a given data structure to share a lock key. Since
lock dependency analysis groups lock objects per key sharing lock keys
can cause false positive lockdep reports. Make it possible to avoid
such false positive reports by allowing lock keys to be allocated
dynamically. Require that dynamically allocated lock keys are
registered before use by calling lockdep_register_key(). Complain about
attempts to register the same lock key pointer twice without calling
lockdep_unregister_key() between successive registration calls.

The purpose of the new lock_keys_hash[] data structure that keeps
track of all dynamic keys is twofold:

  - Verify whether the lockdep_register_key() and lockdep_unregister_key()
    functions are used correctly.

  - Avoid that lockdep_init_map() complains when encountering a dynamically
    allocated key.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: johannes.berg@intel.com
Cc: tj@kernel.org
Link: https://lkml.kernel.org/r/20190214230058.196511-19-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 18 insertions, 3 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 619ec3f26cdc..43fb35bd7baf 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -46,15 +46,19 @@ extern int lock_stat;
 #define NR_LOCKDEP_CACHING_CLASSES      2
 
 /*
- * Lock-classes are keyed via unique addresses, by embedding the
- * lockclass-key into the kernel (or module) .data section. (For
- * static locks we use the lock address itself as the key.)
+ * A lockdep key is associated with each lock object. For static locks we use
+ * the lock address itself as the key. Dynamically allocated lock objects can
+ * have a statically or dynamically allocated key. Dynamically allocated lock
+ * keys must be registered before being used and must be unregistered before
+ * the key memory is freed.
  */
 struct lockdep_subclass_key {
         char __one_byte;
 } __attribute__ ((__packed__));
 
+/* hash_entry is used to keep track of dynamically allocated keys. */
 struct lock_class_key {
+        struct hlist_node               hash_entry;
         struct lockdep_subclass_key     subkeys[MAX_LOCKDEP_SUBCLASSES];
 };
 
@@ -273,6 +277,9 @@ extern void lockdep_set_selftest_task(struct task_struct *task);
 extern void lockdep_off(void);
 extern void lockdep_on(void);
 
+extern void lockdep_register_key(struct lock_class_key *key);
+extern void lockdep_unregister_key(struct lock_class_key *key);
+
 /*
  * These methods are used by specific locking variants (spinlocks,
  * rwlocks, mutexes and rwsems) to pass init/acquire/release events
@@ -434,6 +441,14 @@ static inline void lockdep_set_selftest_task(struct task_struct *task)
  */
 struct lock_class_key { };
 
+static inline void lockdep_register_key(struct lock_class_key *key)
+{
+}
+
+static inline void lockdep_unregister_key(struct lock_class_key *key)
+{
+}
+
 /*
  * The lockdep_map takes no space if lockdep is disabled:
  */