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Subject[patch 15/16] Tracepoints : documentation fix teardown
Need a tracepoint_synchronize_unregister() before the end of exit() to make sure
every probe callers have exited the non preemptible section and thus are not
executing the probe code anymore.

Impact: documentation update.

Signed-off-by: Mathieu Desnoyers <>
CC: Rusty Russell <>
CC: "Frank Ch. Eigler" <>
CC: Ingo Molnar <>
CC: Lai Jiangshan <>
CC: Peter Zijlstra <>
CC: Steven Rostedt <>
Documentation/tracepoints.txt | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
Index: linux-2.6-lttng/Documentation/tracepoints.txt
--- linux-2.6-lttng.orig/Documentation/tracepoints.txt 2008-11-14 17:18:59.000000000 -0500
+++ linux-2.6-lttng/Documentation/tracepoints.txt 2008-11-14 17:19:05.000000000 -0500
@@ -70,10 +70,12 @@ Where :
Connecting a function (probe) to a tracepoint is done by providing a probe
(function to call) for the specific tracepoint through
register_trace_subsys_eventname(). Removing a probe is done through
-unregister_trace_subsys_eventname(); it will remove the probe sure there is no
-caller left using the probe when it returns. Probe removal is preempt-safe
-because preemption is disabled around the probe call. See the "Probe example"
-section below for a sample probe module.
+unregister_trace_subsys_eventname(); it will remove the probe.
+marker_synchronize_unregister() must be called before the end of the module exit
+function to make sure there is no caller left using the probe. This, and the
+fact that preemption is disabled around the probe call, make sure that probe
+removal and module unload are safe. See the "Probe example" section below for a
+sample probe module.

The tracepoint mechanism supports inserting multiple instances of the same
tracepoint, but a single definition must be made of a given tracepoint name over
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68

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