Merge branch 'fixes-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

* 'fixes-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: note the nested NOT_RUNNING test in worker_clr_flags() isn't a noop
  workqueue: relax lockdep annotation on flush_work()

include/linux/lockdep.h

@@ -514,12 +514,15 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
 #  define lock_map_acquire(l)		lock_acquire(l, 0, 0, 0, 2, NULL, _THIS_IP_)
+#  define lock_map_acquire_read(l)	lock_acquire(l, 0, 0, 2, 2, NULL, _THIS_IP_)
 # else
 #  define lock_map_acquire(l)		lock_acquire(l, 0, 0, 0, 1, NULL, _THIS_IP_)
+#  define lock_map_acquire_read(l)	lock_acquire(l, 0, 0, 2, 1, NULL, _THIS_IP_)
 # endif
 # define lock_map_release(l)			lock_release(l, 1, _THIS_IP_)
 #else
 # define lock_map_acquire(l)			do { } while (0)
+# define lock_map_acquire_read(l)		do { } while (0)
 # define lock_map_release(l)			do { } while (0)
 #endif
 

kernel/workqueue.c

@@ -768,7 +768,11 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
 
 	worker->flags &= ~flags;
 
-	/* if transitioning out of NOT_RUNNING, increment nr_running */
+	/*
+	 * If transitioning out of NOT_RUNNING, increment nr_running.  Note
+	 * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
+	 * of multiple flags, not a single flag.
+	 */
 	if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
 		if (!(worker->flags & WORKER_NOT_RUNNING))
 			atomic_inc(get_gcwq_nr_running(gcwq->cpu));
@@ -1840,7 +1844,7 @@ __acquires(&gcwq->lock)
 	spin_unlock_irq(&gcwq->lock);
 
 	work_clear_pending(work);
-	lock_map_acquire(&cwq->wq->lockdep_map);
+	lock_map_acquire_read(&cwq->wq->lockdep_map);
 	lock_map_acquire(&lockdep_map);
 	trace_workqueue_execute_start(work);
 	f(work);
@@ -2384,8 +2388,18 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
 	insert_wq_barrier(cwq, barr, work, worker);
 	spin_unlock_irq(&gcwq->lock);
 
-	lock_map_acquire(&cwq->wq->lockdep_map);
+	/*
+	 * If @max_active is 1 or rescuer is in use, flushing another work
+	 * item on the same workqueue may lead to deadlock.  Make sure the
+	 * flusher is not running on the same workqueue by verifying write
+	 * access.
+	 */
+	if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
+		lock_map_acquire(&cwq->wq->lockdep_map);
+	else
+		lock_map_acquire_read(&cwq->wq->lockdep_map);
 	lock_map_release(&cwq->wq->lockdep_map);
+
 	return true;
 already_gone:
 	spin_unlock_irq(&gcwq->lock);