[PATCH] Markers : fix reentrancy

[Mathieu Desnoyers]

Lai Jiangshan <laijs@xxxxxxxxxxxxxx> wrote :
> marker_synchronize_unregister must be called _also_ between unregistration
> and destruction the data that unregistration-ed probes need to make sure
> there is no caller executing a probe when it's data is destroyed.
> 

Ah, you're right. I looked again through your patch description and I
think using a :


if (entry->rcu_pending)
                rcu_barrier_sched();

After each time the markers_mutex is taken would keep the fast
batch registration/unregistration and fix the reentrancy problem.
The following patch should address the problem.

Thanks,

Mathieu


Lai Jiangshan discovered a reentrancy issue with markers. This patch implements
a version of the fix which won't slow down marker batch
registration/unregistration.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
CC: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
---
 kernel/marker.c |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c	2008-09-30 01:29:18.000000000 -0400
+++ linux-2.6-lttng/kernel/marker.c	2008-09-30 01:31:28.000000000 -0400
@@ -674,6 +674,8 @@ int marker_probe_register(const char *na
 	mutex_lock(&markers_mutex);
 	entry = get_marker(name);
 	WARN_ON(!entry);
+	if (entry->rcu_pending)
+		rcu_barrier_sched();
 	entry->oldptr = old;
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */
@@ -717,6 +719,8 @@ int marker_probe_unregister(const char *
 	entry = get_marker(name);
 	if (!entry)
 		goto end;
+	if (entry->rcu_pending)
+		rcu_barrier_sched();
 	entry->oldptr = old;
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */
@@ -795,6 +799,8 @@ int marker_probe_unregister_private_data
 	mutex_lock(&markers_mutex);
 	entry = get_marker_from_private_data(probe, probe_private);
 	WARN_ON(!entry);
+	if (entry->rcu_pending)
+		rcu_barrier_sched();
 	entry->oldptr = old;
 	entry->rcu_pending = 1;
 	/* write rcu_pending before calling the RCU callback */

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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