Re: [PATCH] markers: comment marker_synchronize_unregister() on data dependency

Wu Fengguang
2008-11-27T08:15:27Z

On Thu, Nov 27, 2008 at 10:00:03AM +0200, Mathieu Desnoyers wrote:
> * Wu Fengguang (fengguang.wu@intel.com) wrote:
> > +
> > +marker_synchronize_unregister() must be called before the first occurrence of
>
>
> You should probably say
>
> ".. must be called between probe unregistration and the first occurence
> of..."
>
> Mathieu

That's much better!

With your comments I'd assume you reviewed this patch ;-)

Thanks,
Fengguang
---
markers: comment marker_synchronize_unregister() on data dependency

Add document and comments on marker_synchronize_unregister(): it
should be called before freeing resources that the probes depend on.

Based on comments from Lai Jiangshan and Mathieu Desnoyers.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
---
diff --git a/Documentation/markers.txt b/Documentation/markers.txt
index 089f613..d9569a3 100644
--- a/Documentation/markers.txt
+++ b/Documentation/markers.txt
@@ -51,11 +51,16 @@ to call) for the specific marker through marker_probe_register() and can be
activated by calling marker_arm(). Marker deactivation can be done by calling
marker_disarm() as many times as marker_arm() has been called. Removing a probe
is done through marker_probe_unregister(); it will disarm the probe.
-marker_synchronize_unregister() must be called before the end of the module exit
-function to make sure there is no caller left using the probe. This, and the
-fact that preemption is disabled around the probe call, make sure that probe
-removal and module unload are safe. See the "Probe example" section below for a
-sample probe module.
+
+marker_synchronize_unregister() must be called between probe unregistration and
+the first occurrence of
+- the end of module exit function,
+ to make sure there is no caller left using the probe;
+- the free of any resource used by the probes,
+ to make sure the probes wont be accessing invalid data.
+This, and the fact that preemption is disabled around the probe call, make sure
+that probe removal and module unload are safe. See the "Probe example" section
+below for a sample probe module.

The marker mechanism supports inserting multiple instances of the same marker.
Markers can be put in inline functions, inlined static functions, and
diff --git a/include/linux/marker.h b/include/linux/marker.h
index 889196c..5f12d1b 100644
--- a/include/linux/marker.h
+++ b/include/linux/marker.h
@@ -162,8 +162,10 @@ 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.
+ * unregistration and the first one of
+ * - the end of module exit function
+ * - the free of any resource used by the probes
+ * to ensure the code and data are valid for any possibly running probes.