3 files changed, 39 insertions, 6 deletions

diff --git a/kernel/async.c b/kernel/async.c
index 9d3118384858..a1d585c351d6 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 250092c1d57d..b10b048367e1 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 1bbfa0446507..3c13e46d7d24 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)++;