[PATCH v6 03/16] locking/lockdep: Make zap_class() remove all matching lock order entries

[Bart Van Assche]

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.

Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Waiman Long <long...@redhat.com>
Cc: Johannes Berg <johan...@sipsolutions.net>
Signed-off-by: Bart Van Assche <bvanass...@acm.org>
---
 include/linux/lockdep.h  |  1 +
 kernel/locking/lockdep.c | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c5335df2372f..71caa1118f4c 100644
--- a/include/linux/lockdep.h
+++ b/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;
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7a7c2d7b01c2..e52ce8745cba 100644
--- a/kernel/locking/lockdep.c
+++ b/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;
        /*
@@ -1918,14 +1920,14 @@ 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)
@@ -4119,15 +4121,20 @@ 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:
-- 
2.20.1.97.g81188d93c3-goog