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Subject[PATCH] Markers : fix reentrancy
Lai Jiangshan <laijs@cn.fujitsu.com> 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@polymtl.ca>
CC: Ingo Molnar <mingo@elte.hu>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
CC: "Frank Ch. Eigler" <fche@redhat.com>
---
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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