[PATCH for 2.6.25] Markers - use synchronize_sched()

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@xxxxxxxxxx>
CC: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
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
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