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markers: comment marker_synchronize_unregister() on data dependency 

Add document and comments on marker_synchronize_unregister(): it
should be called before freeing resources that the probes depend on.

Based on comments from Lai Jiangshan and Mathieu Desnoyers.

Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Wu Fengguang 2008-11-27 16:14:44 +08:00 committed by Ingo Molnar
parent c7cc773076
commit a838c2ec6e
2 changed files with 14 additions and 7 deletions
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15
Documentation/markers.txt
View File

@ -51,11 +51,16 @@ to call) for the specific marker through marker_probe_register() and can be
activated by calling marker_arm(). Marker deactivation can be done by calling
marker_disarm() as many times as marker_arm() has been called. Removing a probe
is done through marker_probe_unregister(); it will disarm 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.
marker_synchronize_unregister() must be called between probe unregistration and
the first occurrence of
- the end of module exit function,
to make sure there is no caller left using the probe;
- the free of any resource used by the probes,
to make sure the probes wont be accessing invalid data.
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 marker mechanism supports inserting multiple instances of the same marker.
Markers can be put in inline functions, inlined static functions, and

6
include/linux/marker.h
View File

@ -211,8 +211,10 @@ extern void *marker_get_private_data(const char *name, marker_probe_func *probe,
/*
* marker_synchronize_unregister must be called between the last marker probe
* unregistration and the end of module exit to make sure there is no caller
* executing a probe when it is freed.
* unregistration and the first one of
* - the end of module exit function
* - the free of any resource used by the probes
* to ensure the code and data are valid for any possibly running probes.
*/
#define marker_synchronize_unregister() synchronize_sched()