linux-kernel - Re: [PATCH] markers: comment marker_synchronize

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Date:	Thu, 27 Nov 2008 16:14:44 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Avi Kivity <avi@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] markers: comment marker_synchronize_unregister() on
	data dependency

On Thu, Nov 27, 2008 at 10:00:03AM +0200, Mathieu Desnoyers wrote:
> * Wu Fengguang (fengguang.wu@...el.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@...ymtl.ca>
Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com>
Signed-off-by: Wu Fengguang <wfg@...ux.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.
  */
 #define marker_synchronize_unregister() synchronize_sched()
 
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