[PATCH for 2.6.25] Markers - use synchronize_sched()

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

Use synchronize_sched before calling call_rcu in CONFIG_PREEMPT_RCU until we
have call_rcu_sched and rcu_barrier_sched in mainline. It will slow down the
marker operations in CONFIG_PREEMPT_RCU, but it fixes the current race against
the preempt_disable/enable() protected code paths.

Paul, is this ok ? It would be good to get this in for 2.6.25 final.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/marker.c |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c	2008-03-31 08:22:24.000000000 -0400
+++ linux-2.6-lttng/kernel/marker.c	2008-03-31 08:43:30.000000000 -0400
@@ -671,6 +671,9 @@ int marker_probe_register(const char *na
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */
 	smp_wmb();
+#ifdef CONFIG_PREEMPT_RCU
+	synchronize_sched();	/* Until we have the call_rcu_sched() */
+#endif
 	call_rcu(&entry->rcu, free_old_closure);
 end:
 	mutex_unlock(&markers_mutex);
@@ -714,6 +717,9 @@ int marker_probe_unregister(const char *
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */
 	smp_wmb();
+#ifdef CONFIG_PREEMPT_RCU
+	synchronize_sched();	/* Until we have the call_rcu_sched() */
+#endif
 	call_rcu(&entry->rcu, free_old_closure);
 	remove_marker(name);	/* Ignore busy error message */
 	ret = 0;
@@ -792,6 +798,9 @@ int marker_probe_unregister_private_data
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */
 	smp_wmb();
+#ifdef CONFIG_PREEMPT_RCU
+	synchronize_sched();	/* Until we have the call_rcu_sched() */
+#endif
 	call_rcu(&entry->rcu, free_old_closure);
 	remove_marker(entry->name);	/* Ignore busy error message */
 end:
-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68