3 files changed, 39 insertions, 6 deletions

diff --git a/kernel/async.c b/kernel/async.c
index 9d311838485..a1d585c351d 100644
--- a/kernel/async.c
+++ b/kernel/async.c
@@ -196,6 +196,9 @@ static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct a
 	atomic_inc(&entry_count);
 	spin_unlock_irqrestore(&async_lock, flags);
 
+	/* mark that this task has queued an async job, used by module init */
+	current->flags |= PF_USED_ASYNC;
+
 	/* schedule for execution */
 	queue_work(system_unbound_wq, &entry->work);
 
diff --git a/kernel/module.c b/kernel/module.c
index 250092c1d57..b10b048367e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3013,6 +3013,12 @@ static int do_init_module(struct module *mod)
 {
 	int ret = 0;
 
+	/*
+	 * We want to find out whether @mod uses async during init.  Clear
+	 * PF_USED_ASYNC.  async_schedule*() will set it.
+	 */
+	current->flags &= ~PF_USED_ASYNC;
+
 	blocking_notifier_call_chain(&module_notify_list,
 			MODULE_STATE_COMING, mod);
 
@@ -3058,8 +3064,25 @@ static int do_init_module(struct module *mod)
 	blocking_notifier_call_chain(&module_notify_list,
 				     MODULE_STATE_LIVE, mod);
 
-	/* We need to finish all async code before the module init sequence is done */
-	async_synchronize_full();
+	/*
+	 * We need to finish all async code before the module init sequence
+	 * is done.  This has potential to deadlock.  For example, a newly
+	 * detected block device can trigger request_module() of the
+	 * default iosched from async probing task.  Once userland helper
+	 * reaches here, async_synchronize_full() will wait on the async
+	 * task waiting on request_module() and deadlock.
+	 *
+	 * This deadlock is avoided by perfomring async_synchronize_full()
+	 * iff module init queued any async jobs.  This isn't a full
+	 * solution as it will deadlock the same if module loading from
+	 * async jobs nests more than once; however, due to the various
+	 * constraints, this hack seems to be the best option for now.
+	 * Please refer to the following thread for details.
+	 *
+	 * http://thread.gmane.org/gmane.linux.kernel/1420814
+	 */
+	if (current->flags & PF_USED_ASYNC)
+		async_synchronize_full();
 
 	mutex_lock(&module_mutex);
 	/* Drop initial reference. */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1bbfa044650..3c13e46d7d2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3454,7 +3454,7 @@ static int tracing_wait_pipe(struct file *filp)
 			return -EINTR;
 
 		/*
-		 * We block until we read something and tracing is enabled.
+		 * We block until we read something and tracing is disabled.
 		 * We still block if tracing is disabled, but we have never
 		 * read anything. This allows a user to cat this file, and
 		 * then enable tracing. But after we have read something,
@@ -3462,7 +3462,7 @@ static int tracing_wait_pipe(struct file *filp)
 		 *
 		 * iter->pos will be 0 if we haven't read anything.
 		 */
-		if (tracing_is_enabled() && iter->pos)
+		if (!tracing_is_enabled() && iter->pos)
 			break;
 	}
 
@@ -4817,10 +4817,17 @@ rb_simple_write(struct file *filp, const char __user *ubuf,
 		return ret;
 
 	if (buffer) {
-		if (val)
+		mutex_lock(&trace_types_lock);
+		if (val) {
 			ring_buffer_record_on(buffer);
-		else
+			if (current_trace->start)
+				current_trace->start(tr);
+		} else {
 			ring_buffer_record_off(buffer);
+			if (current_trace->stop)
+				current_trace->stop(tr);
+		}
+		mutex_unlock(&trace_types_lock);
 	}
 
 	(*ppos)++;