locking/lockdep: Make zap_class() remove all matching lock order entries

Make sure that all lock order entries that refer to a class are removed
from the list_entries[] array when a kernel module is unloaded.
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/20190214230058.196511-7-bvanassche@acm.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/lockdep.h

@@ -178,6 +178,7 @@ static inline void lockdep_copy_map(struct lockdep_map *to,
 struct lock_list {
 	struct list_head		entry;
 	struct lock_class		*class;
+	struct lock_class		*links_to;
 	struct stack_trace		trace;
 	int				distance;
 

kernel/locking/lockdep.c

@@ -859,7 +859,8 @@ static struct lock_list *alloc_list_entry(void)
 /*
  * Add a new dependency to the head of the list:
  */
-static int add_lock_to_list(struct lock_class *this, struct list_head *head,
+static int add_lock_to_list(struct lock_class *this,
+			    struct lock_class *links_to, struct list_head *head,
 			    unsigned long ip, int distance,
 			    struct stack_trace *trace)
 {
@@ -873,6 +874,7 @@ static int add_lock_to_list(struct lock_class *this, struct list_head *head,
 		return 0;
 
 	entry->class = this;
+	entry->links_to = links_to;
 	entry->distance = distance;
 	entry->trace = *trace;
 	/*
@@ -1907,14 +1909,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 * Ok, all validations passed, add the new lock
 	 * to the previous lock's dependency list:
 	 */
-	ret = add_lock_to_list(hlock_class(next),
+	ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
 			       &hlock_class(prev)->locks_after,
 			       next->acquire_ip, distance, trace);
 
 	if (!ret)
 		return 0;
 
-	ret = add_lock_to_list(hlock_class(prev),
+	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
 			       &hlock_class(next)->locks_before,
 			       next->acquire_ip, distance, trace);
 	if (!ret)
@@ -4107,15 +4109,20 @@ void lockdep_reset(void)
  */
 static void zap_class(struct lock_class *class)
 {
+	struct lock_list *entry;
 	int i;
 
 	/*
 	 * Remove all dependencies this lock is
 	 * involved in:
 	 */
-	for (i = 0; i < nr_list_entries; i++) {
-		if (list_entries[i].class == class)
-			list_del_rcu(&list_entries[i].entry);
+	for (i = 0, entry = list_entries; i < nr_list_entries; i++, entry++) {
+		if (entry->class != class && entry->links_to != class)
+			continue;
+		list_del_rcu(&entry->entry);
+		/* Clear .class and .links_to to avoid double removal. */
+		WRITE_ONCE(entry->class, NULL);
+		WRITE_ONCE(entry->links_to, NULL);
 	}
 	/*
 	 * Unhash the class and remove it from the all_lock_classes list: