[patch 2/4] Markers - Update preempt_disable. call_rcu, rcu_barrier comments.

[Mathieu Desnoyers]

Add comments requested by Andrew.
Updated comments about synchronize_sched(). Since we use call_rcu and
rcu_barrier now, these comments were out of sync with the code.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Christoph Hellwig <hch@xxxxxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxx>
CC: Mike Mason <mmlnx@xxxxxxxxxx>
CC: Dipankar Sarma <dipankar@xxxxxxxxxx>
CC: David Smith <dsmith@xxxxxxxxxx>
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Adrian Bunk <adrian.bunk@xxxxxxxxx>
---
 kernel/marker.c |   19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c	2008-03-19 18:26:47.000000000 -0400
+++ linux-2.6-lttng/kernel/marker.c	2008-03-19 18:30:26.000000000 -0400
@@ -104,9 +104,9 @@ void marker_probe_cb(const struct marker
 	char ptype;
 
 	/*
-	 * disabling preemption to make sure the teardown of the callbacks can
-	 * be done correctly when they are in modules and they insure RCU read
-	 * coherency.
+	 * preempt_disable does two things : disabling preemption to make sure
+	 * the teardown of the callbacks can be done correctly when they are in
+	 * modules and they insure RCU read coherency.
 	 */
 	preempt_disable();
 	ptype = ACCESS_ONCE(mdata->ptype);
@@ -551,9 +551,9 @@ static int set_marker(struct marker_entr
 
 /*
  * Disable a marker and its probe callback.
- * Note: only after a synchronize_sched() issued after setting elem->call to the
- * empty function insures that the original callback is not used anymore. This
- * insured by preemption disabling around the call site.
+ * Note: only waiting an RCU period after setting elem->call to the empty
+ * function insures that the original callback is not used anymore. This insured
+ * by preempt_disable around the call site.
  */
 static void disable_marker(struct marker *elem)
 {
@@ -565,8 +565,8 @@ static void disable_marker(struct marker
 	elem->ptype = 0;	/* single probe */
 	/*
 	 * Leave the private data and id there, because removal is racy and
-	 * should be done only after a synchronize_sched(). These are never used
-	 * until the next initialization anyway.
+	 * should be done only after an RCU period. These are never used until
+	 * the next initialization anyway.
 	 */
 }
 
@@ -601,9 +601,6 @@ void marker_update_probe_range(struct ma
 
 /*
  * Update probes, removing the faulty probes.
- * Issues a synchronize_sched() when no reference to the module passed
- * as parameter is found in the probes so the probe module can be
- * safely unloaded from now on.
  *
  * Internal callback only changed before the first probe is connected to it.
  * Single probe private data can only be changed on 0 -> 1 and 2 -> 1

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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