1 files changed, 29 insertions, 13 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index d6459923d245..fd6198692b57 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -404,6 +404,11 @@ static void timer_stats_account_timer(struct timer_list *timer) {}
 
 static struct debug_obj_descr timer_debug_descr;
 
+static void *timer_debug_hint(void *addr)
+{
+        return ((struct timer_list *) addr)->function;
+}
+
 /*
  * fixup_init is called when:
  * - an active object is initialized
@@ -477,6 +482,7 @@ static int timer_fixup_free(void *addr, enum debug_obj_state state)
 
 static struct debug_obj_descr timer_debug_descr = {
         .name           = "timer_list",
+        .debug_hint     = timer_debug_hint,
         .fixup_init     = timer_fixup_init,
         .fixup_activate = timer_fixup_activate,
         .fixup_free     = timer_fixup_free,
@@ -964,6 +970,25 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
  * add_timer_on(). Upon exit the timer is not queued and the handler is
  * not running on any CPU.
  *
+ * Note: You must not hold locks that are held in interrupt context
+ *   while calling this function. Even if the lock has nothing to do
+ *   with the timer in question.  Here's why:
+ *
+ *    CPU0                             CPU1
+ *    ----                             ----
+ *                                   <SOFTIRQ>
+ *                                   call_timer_fn();
+ *                                     base->running_timer = mytimer;
+ *  spin_lock_irq(somelock);
+ *                                     <IRQ>
+ *                                        spin_lock(somelock);
+ *  del_timer_sync(mytimer);
+ *   while (base->running_timer == mytimer);
+ *
+ * Now del_timer_sync() will never return and never release somelock.
+ * The interrupt on the other CPU is waiting to grab somelock but
+ * it has interrupted the softirq that CPU0 is waiting to finish.
+ *
  * The function returns whether it has deactivated a pending timer or not.
  */
 int del_timer_sync(struct timer_list *timer)
@@ -971,6 +996,10 @@ int del_timer_sync(struct timer_list *timer)
 #ifdef CONFIG_LOCKDEP
         unsigned long flags;
 
+        /*
+         * If lockdep gives a backtrace here, please reference
+         * the synchronization rules above.
+         */
         local_irq_save(flags);
         lock_map_acquire(&timer->lockdep_map);
         lock_map_release(&timer->lockdep_map);
@@ -1295,19 +1324,6 @@ void run_local_timers(void)
         raise_softirq(TIMER_SOFTIRQ);
 }
 
-/*
- * The 64-bit jiffies value is not atomic - you MUST NOT read it
- * without sampling the sequence number in xtime_lock.
- * jiffies is defined in the linker script...
- */
-
-void do_timer(unsigned long ticks)
-{
-        jiffies_64 += ticks;
-        update_wall_time();
-        calc_global_load(ticks);
-}
-
 #ifdef __ARCH_WANT_SYS_ALARM
 
 /*