[PATCH v2 02/17] locking/lockdep: Rework lockdep_set_novalidate_class()

Waiman Long
2018-11-19T18:56:57Z

The current lockdep_set_novalidate_class() implementation is like
a hack. It assigns a special class key for that lock and calls
lockdep_init_map() twice.

This patch changes the implementation to make it as a flag bit instead.
This will allow other special locking class types to be defined and
used in the lockdep code. A new "type" field is added to both the
lockdep_map and lock_class structures.

The new field can now be used to designate a lock and a class object
as novalidate. The lockdep_set_novalidate_class() call, however, should
be called only after lock initialization which calls lockdep_init_map().

For 64-bit architectures, the new type field won't increase the size
of the lock_class structure. The lockdep_map structure won't change as
well for 64-bit architectures with CONFIG_LOCK_STAT configured.

Please note that lockdep_set_novalidate_class() should not be used at
all unless there is overwhelming reason to do so. Hopefully we can
retired it in the near future.

Signed-off-by: Waiman Long <longman@redhat.com>
---
include/linux/lockdep.h | 17 ++++++++++++++---
kernel/locking/lockdep.c | 14 +++++++-------
2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c5335df..8fe5b4f 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -58,8 +58,6 @@ struct lock_class_key {
struct lockdep_subclass_key subkeys[MAX_LOCKDEP_SUBCLASSES];
};

-extern struct lock_class_key __lockdep_no_validate__;
-
#define LOCKSTAT_POINTS 4

/*
@@ -94,6 +92,11 @@ struct lock_class {
struct list_head locks_after, locks_before;

/*
+ * Lock class type flags
+ */
+ unsigned int flags;
+
+ /*
* Generation counter, when doing certain classes of graph walking,
* to ensure that we check one node only once:
*/
@@ -140,6 +143,12 @@ struct lock_class_stats {
#endif

/*
+ * Lockdep class type flags
+ * 1) LOCKDEP_FLAG_NOVALIDATE: No full validation, just simple checks.
+ */
+#define LOCKDEP_FLAG_NOVALIDATE (1 << 0)
+
+/*
* Map the lock object (the lock instance) to the lock-class object.
* This is embedded into specific lock instances:
*/
@@ -147,6 +156,7 @@ struct lockdep_map {
struct lock_class_key *key;
struct lock_class *class_cache[NR_LOCKDEP_CACHING_CLASSES];
const char *name;
+ unsigned int flags;
#ifdef CONFIG_LOCK_STAT
int cpu;
unsigned long ip;
@@ -294,7 +304,8 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
(lock)->dep_map.key, sub)

#define lockdep_set_novalidate_class(lock) \
- lockdep_set_class_and_name(lock, &__lockdep_no_validate__, #lock)
+ do { (lock)->dep_map.flags |= LOCKDEP_FLAG_NOVALIDATE; } while (0)
+
/*
* Compare locking classes
*/
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1efada2..493b567 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -692,10 +692,11 @@ static int count_matching_names(struct lock_class *new_class)
hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
if (class->key == key) {
/*
- * Huh! same key, different name? Did someone trample
- * on some memory? We're most confused.
+ * Huh! same key, different name or flags? Did someone
+ * trample on some memory? We're most confused.
*/
- WARN_ON_ONCE(class->name != lock->name);
+ WARN_ON_ONCE((class->name != lock->name) ||
+ (class->flags != lock->flags));
return class;
}
}
@@ -788,6 +789,7 @@ static bool assign_lock_key(struct lockdep_map *lock)
debug_atomic_inc(nr_unused_locks);
class->key = key;
class->name = lock->name;
+ class->flags = lock->flags;
class->subclass = subclass;
INIT_LIST_HEAD(&class->lock_entry);
INIT_LIST_HEAD(&class->locks_before);
@@ -3108,6 +3110,7 @@ static void __lockdep_init_map(struct lockdep_map *lock, const char *name,
return;
}

+ lock->flags = 0;
lock->name = name;

/*
@@ -3152,9 +3155,6 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
}
EXPORT_SYMBOL_GPL(lockdep_init_map);

-struct lock_class_key __lockdep_no_validate__;
-EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
-
static int
print_lock_nested_lock_not_held(struct task_struct *curr,
struct held_lock *hlock,
@@ -3215,7 +3215,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (unlikely(!debug_locks))
return 0;

- if (!prove_locking || lock->key == &__lockdep_no_validate__)
+ if (!prove_locking || (lock->flags & LOCKDEP_FLAG_NOVALIDATE))
check = 0;

if (subclass < NR_LOCKDEP_CACHING_CLASSES)
--
1.8.3.1