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authorBart Van Assche <bvanassche@acm.org>2019-02-14 15:00:53 -0800
committerIngo Molnar <mingo@kernel.org>2019-02-28 07:55:47 +0100
commit108c14858b9ea224686e476c8f5ec345a0df9e27 (patch)
treeada6db8dd14a4bb2ee10d5664ac9ae4dd55cc32f /kernel/locking
parent4bf508621855613ca2ac782f70c3171e0e8bb011 (diff)
downloadlinux-108c14858b9ea224686e476c8f5ec345a0df9e27.tar.bz2
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>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep.c121
1 files changed, 113 insertions, 8 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 84427441824e..c73bc4334bee 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -143,6 +143,9 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
* nr_lock_classes is the number of elements of lock_classes[] that is
* in use.
*/
+#define KEYHASH_BITS (MAX_LOCKDEP_KEYS_BITS - 1)
+#define KEYHASH_SIZE (1UL << KEYHASH_BITS)
+static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
unsigned long nr_lock_classes;
#ifndef CONFIG_DEBUG_LOCKDEP
static
@@ -641,7 +644,7 @@ static int very_verbose(struct lock_class *class)
* Is this the address of a static object:
*/
#ifdef __KERNEL__
-static int static_obj(void *obj)
+static int static_obj(const void *obj)
{
unsigned long start = (unsigned long) &_stext,
end = (unsigned long) &_end,
@@ -975,6 +978,71 @@ static void init_data_structures_once(void)
}
}
+static inline struct hlist_head *keyhashentry(const struct lock_class_key *key)
+{
+ unsigned long hash = hash_long((uintptr_t)key, KEYHASH_BITS);
+
+ return lock_keys_hash + hash;
+}
+
+/* Register a dynamically allocated key. */
+void lockdep_register_key(struct lock_class_key *key)
+{
+ struct hlist_head *hash_head;
+ struct lock_class_key *k;
+ unsigned long flags;
+
+ if (WARN_ON_ONCE(static_obj(key)))
+ return;
+ hash_head = keyhashentry(key);
+
+ raw_local_irq_save(flags);
+ if (!graph_lock())
+ goto restore_irqs;
+ hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
+ if (WARN_ON_ONCE(k == key))
+ goto out_unlock;
+ }
+ hlist_add_head_rcu(&key->hash_entry, hash_head);
+out_unlock:
+ graph_unlock();
+restore_irqs:
+ raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lockdep_register_key);
+
+/* Check whether a key has been registered as a dynamic key. */
+static bool is_dynamic_key(const struct lock_class_key *key)
+{
+ struct hlist_head *hash_head;
+ struct lock_class_key *k;
+ bool found = false;
+
+ if (WARN_ON_ONCE(static_obj(key)))
+ return false;
+
+ /*
+ * If lock debugging is disabled lock_keys_hash[] may contain
+ * pointers to memory that has already been freed. Avoid triggering
+ * a use-after-free in that case by returning early.
+ */
+ if (!debug_locks)
+ return true;
+
+ hash_head = keyhashentry(key);
+
+ rcu_read_lock();
+ hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
+ if (k == key) {
+ found = true;
+ break;
+ }
+ }
+ rcu_read_unlock();
+
+ return found;
+}
+
/*
* Register a lock's class in the hash-table, if the class is not present
* yet. Otherwise we look it up. We cache the result in the lock object
@@ -996,7 +1064,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
if (!lock->key) {
if (!assign_lock_key(lock))
return NULL;
- } else if (!static_obj(lock->key)) {
+ } else if (!static_obj(lock->key) && !is_dynamic_key(lock->key)) {
return NULL;
}
@@ -3378,13 +3446,12 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
if (DEBUG_LOCKS_WARN_ON(!key))
return;
/*
- * Sanity check, the lock-class key must be persistent:
+ * Sanity check, the lock-class key must either have been allocated
+ * statically or must have been registered as a dynamic key.
*/
- if (!static_obj(key)) {
- printk("BUG: key %px not in .data!\n", key);
- /*
- * What it says above ^^^^^, I suggest you read it.
- */
+ if (!static_obj(key) && !is_dynamic_key(key)) {
+ if (debug_locks)
+ printk(KERN_ERR "BUG: key %px has not been registered!\n", key);
DEBUG_LOCKS_WARN_ON(1);
return;
}
@@ -4795,6 +4862,44 @@ void lockdep_reset_lock(struct lockdep_map *lock)
lockdep_reset_lock_reg(lock);
}
+/* Unregister a dynamically allocated key. */
+void lockdep_unregister_key(struct lock_class_key *key)
+{
+ struct hlist_head *hash_head = keyhashentry(key);
+ struct lock_class_key *k;
+ struct pending_free *pf;
+ unsigned long flags;
+ bool found = false;
+
+ might_sleep();
+
+ if (WARN_ON_ONCE(static_obj(key)))
+ return;
+
+ raw_local_irq_save(flags);
+ if (!graph_lock())
+ goto out_irq;
+
+ pf = get_pending_free();
+ hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
+ if (k == key) {
+ hlist_del_rcu(&k->hash_entry);
+ found = true;
+ break;
+ }
+ }
+ WARN_ON_ONCE(!found);
+ __lockdep_free_key_range(pf, key, 1);
+ call_rcu_zapped(pf);
+ graph_unlock();
+out_irq:
+ raw_local_irq_restore(flags);
+
+ /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(lockdep_unregister_key);
+
void __init lockdep_init(void)
{
printk("Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar\n");