From fb7275acd6fb988313dddd8d3d19efa70d9015ad Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Thu, 10 Feb 2022 22:55:26 -0500 Subject: locking/lockdep: Iterate lock_classes directly when reading lockdep files When dumping lock_classes information via /proc/lockdep, we can't take the lockdep lock as the lock hold time is indeterminate. Iterating over all_lock_classes without holding lock can be dangerous as there is a slight chance that it may branch off to other lists leading to infinite loop or even access invalid memory if changes are made to all_lock_classes list in parallel. To avoid this problem, iteration of lock classes is now done directly on the lock_classes array itself. The lock_classes_in_use bitmap is checked to see if the lock class is being used. To avoid iterating the full array all the times, a new max_lock_class_idx value is added to track the maximum lock_class index that is currently being used. We can theoretically take the lockdep lock for iterating all_lock_classes when other lockdep files (lockdep_stats and lock_stat) are accessed as the lock hold time will be shorter for them. For consistency, they are also modified to iterate the lock_classes array directly. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220211035526.1329503-2-longman@redhat.com --- kernel/locking/lockdep.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) (limited to 'kernel/locking/lockdep.c') diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 2e6892ec3756..50036c10b518 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -183,11 +183,9 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES); static struct hlist_head lock_keys_hash[KEYHASH_SIZE]; unsigned long nr_lock_classes; unsigned long nr_zapped_classes; -#ifndef CONFIG_DEBUG_LOCKDEP -static -#endif +unsigned long max_lock_class_idx; struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; -static DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS); +DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS); static inline struct lock_class *hlock_class(struct held_lock *hlock) { @@ -338,7 +336,7 @@ static inline void lock_release_holdtime(struct held_lock *hlock) * elements. These elements are linked together by the lock_entry member in * struct lock_class. */ -LIST_HEAD(all_lock_classes); +static LIST_HEAD(all_lock_classes); static LIST_HEAD(free_lock_classes); /** @@ -1252,6 +1250,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) struct lockdep_subclass_key *key; struct hlist_head *hash_head; struct lock_class *class; + int idx; DEBUG_LOCKS_WARN_ON(!irqs_disabled()); @@ -1317,6 +1316,9 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) * of classes. */ list_move_tail(&class->lock_entry, &all_lock_classes); + idx = class - lock_classes; + if (idx > max_lock_class_idx) + max_lock_class_idx = idx; if (verbose(class)) { graph_unlock(); @@ -6000,6 +6002,8 @@ static void zap_class(struct pending_free *pf, struct lock_class *class) WRITE_ONCE(class->name, NULL); nr_lock_classes--; __clear_bit(class - lock_classes, lock_classes_in_use); + if (class - lock_classes == max_lock_class_idx) + max_lock_class_idx--; } else { WARN_ONCE(true, "%s() failed for class %s\n", __func__, class->name); -- cgit v1.2.3