[PATCH] markers: comment usage of marker_synchronize_unregister()

[Wu Fengguang <fengguang.wu@intel.com>]

Add more comments to marker_synchronize_unregister() in order to
reduce the chance of misusing.

Based on comments from Lai Jiangshan <laijs@cn.fujitsu.com>.

Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
---

I'm still not sure about the last sentence. Can anyone clarify on
this? Thanks!

diff --git a/include/linux/marker.h b/include/linux/marker.h
index 889196c..89ce1b8 100644
--- a/include/linux/marker.h
+++ b/include/linux/marker.h
@@ -164,6 +164,12 @@ extern void *marker_get_private_data(const char *name, marker_probe_func *probe,
  * marker_synchronize_unregister must be called between the last marker probe
  * unregistration and the end of module exit to make sure there is no caller
  * executing a probe when it is freed.
+ *
+ * It must be called _also_ between unregistration and destruction the data
+ * that unregistration-ed probes need to make sure there is no caller executing
+ * a probe when it's data is destroyed.
+ *
+ * It works reliably only when all probe routines do not sleep and reschedule.
  */
 #define marker_synchronize_unregister() synchronize_sched()