Re: [PATCH] markers: comment marker_synchronize_unregister() on data dependency

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Wu Fengguang wrote:
> [updated patch to include Documentation/markers.txt changes]
> 
> 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.
> 
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
> ---
> diff --git a/Documentation/markers.txt b/Documentation/markers.txt
> index 089f613..8bf6afe 100644
> --- a/Documentation/markers.txt
> +++ b/Documentation/markers.txt
> @@ -51,11 +51,15 @@ 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 before the first occurrence of
> +- the end of the 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 destructed 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
> diff --git a/include/linux/marker.h b/include/linux/marker.h
> index 889196c..32ce4f2 100644
> --- a/include/linux/marker.h
> +++ b/include/linux/marker.h
> @@ -162,8 +162,10 @@ 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

Does "destruction" contain the meaning of "free" and other destruction behavior?

It's every good job, thank you.

Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

> + * to ensure the code and data are valid for any possibly running probes.
>   */
>  #define marker_synchronize_unregister() synchronize_sched()
>  
> 


> 
>