timer: implement lockdep deadlock detection

This modifies the timer code in a way to allow lockdep to detect
deadlocks resulting from a lock being taken in the timer function
as well as around the del_timer_sync() call.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

1 files changed, 57 insertions, 11 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index 13dd64fe143d..ef1c385bc572 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -491,14 +491,18 @@ static inline void debug_timer_free(struct timer_list *timer)
         debug_object_free(timer, &timer_debug_descr);
 }
 
-static void __init_timer(struct timer_list *timer);
+static void __init_timer(struct timer_list *timer,
+                         const char *name,
+                         struct lock_class_key *key);
 
-void init_timer_on_stack(struct timer_list *timer)
+void init_timer_on_stack_key(struct timer_list *timer,
+                             const char *name,
+                             struct lock_class_key *key)
 {
         debug_object_init_on_stack(timer, &timer_debug_descr);
-        __init_timer(timer);
+        __init_timer(timer, name, key);
 }
-EXPORT_SYMBOL_GPL(init_timer_on_stack);
+EXPORT_SYMBOL_GPL(init_timer_on_stack_key);
 
 void destroy_timer_on_stack(struct timer_list *timer)
 {
@@ -512,7 +516,9 @@ static inline void debug_timer_activate(struct timer_list *timer) { }
 static inline void debug_timer_deactivate(struct timer_list *timer) { }
 #endif
 
-static void __init_timer(struct timer_list *timer)
+static void __init_timer(struct timer_list *timer,
+                         const char *name,
+                         struct lock_class_key *key)
 {
         timer->entry.next = NULL;
         timer->base = __raw_get_cpu_var(tvec_bases);
@@ -521,6 +527,7 @@ static void __init_timer(struct timer_list *timer)
         timer->start_pid = -1;
         memset(timer->start_comm, 0, TASK_COMM_LEN);
 #endif
+        lockdep_init_map(&timer->lockdep_map, name, key, 0);
 }
 
 /**
@@ -530,19 +537,23 @@ static void __init_timer(struct timer_list *timer)
  * init_timer() must be done to a timer prior calling *any* of the
  * other timer functions.
  */
-void init_timer(struct timer_list *timer)
+void init_timer_key(struct timer_list *timer,
+                    const char *name,
+                    struct lock_class_key *key)
 {
         debug_timer_init(timer);
-        __init_timer(timer);
+        __init_timer(timer, name, key);
 }
-EXPORT_SYMBOL(init_timer);
+EXPORT_SYMBOL(init_timer_key);
 
-void init_timer_deferrable(struct timer_list *timer)
+void init_timer_deferrable_key(struct timer_list *timer,
+                               const char *name,
+                               struct lock_class_key *key)
 {
-        init_timer(timer);
+        init_timer_key(timer, name, key);
         timer_set_deferrable(timer);
 }
-EXPORT_SYMBOL(init_timer_deferrable);
+EXPORT_SYMBOL(init_timer_deferrable_key);
 
 static inline void detach_timer(struct timer_list *timer,
                                 int clear_pending)
@@ -789,6 +800,15 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
  */
 int del_timer_sync(struct timer_list *timer)
 {
+#ifdef CONFIG_LOCKDEP
+        unsigned long flags;
+
+        local_irq_save(flags);
+        lock_map_acquire(&timer->lockdep_map);
+        lock_map_release(&timer->lockdep_map);
+        local_irq_restore(flags);
+#endif
+
         for (;;) {
                 int ret = try_to_del_timer_sync(timer);
                 if (ret >= 0)
@@ -861,10 +881,36 @@ static inline void __run_timers(struct tvec_base *base)
 
                         set_running_timer(base, timer);
                         detach_timer(timer, 1);
+
                         spin_unlock_irq(&base->lock);
                         {
                                 int preempt_count = preempt_count();
+
+#ifdef CONFIG_LOCKDEP
+                                /*
+                                 * It is permissible to free the timer from
+                                 * inside the function that is called from
+                                 * it, this we need to take into account for
+                                 * lockdep too. To avoid bogus "held lock
+                                 * freed" warnings as well as problems when
+                                 * looking into timer->lockdep_map, make a
+                                 * copy and use that here.
+                                 */
+                                struct lockdep_map lockdep_map =
+                                        timer->lockdep_map;
+#endif
+                                /*
+                                 * Couple the lock chain with the lock chain at
+                                 * del_timer_sync() by acquiring the lock_map
+                                 * around the fn() call here and in
+                                 * del_timer_sync().
+                                 */
+                                lock_map_acquire(&lockdep_map);
+
                                 fn(data);
+
+                                lock_map_release(&lockdep_map);
+
                                 if (preempt_count != preempt_count()) {
                                         printk(KERN_ERR "huh, entered %p "
                                                "with preempt_count %08x, exited"