linux-kernel - Re: [PATCH] markers: comment marker_synchronize

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Date:	Thu, 27 Nov 2008 13:44:03 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Avi Kivity <avi@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] markers: comment marker_synchronize_unregister() on
	data dependency

* Wu Fengguang (fengguang.wu@...el.com) wrote:
> On Thu, Nov 27, 2008 at 10:00:03AM +0200, Mathieu Desnoyers wrote:
> > * Wu Fengguang (fengguang.wu@...el.com) wrote:
> > > +
> > > +marker_synchronize_unregister() must be called before the first occurrence of
> > 
> > 
> > You should probably say 
> > 
> > ".. must be called between probe unregistration and the first occurence
> > of..."
> > 
> > Mathieu
> 
> That's much better!
> 
> With your comments I'd assume you reviewed this patch ;-)
> 
> Thanks,
> Fengguang
> ---
> 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.
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com>
> Signed-off-by: Wu Fengguang <wfg@...ux.intel.com>

It looks good to me, thanks!

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>


> ---
> diff --git a/Documentation/markers.txt b/Documentation/markers.txt
> index 089f613..d9569a3 100644
> --- a/Documentation/markers.txt
> +++ b/Documentation/markers.txt
> @@ -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
> diff --git a/include/linux/marker.h b/include/linux/marker.h
> index 889196c..5f12d1b 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
> + * to ensure the code and data are valid for any possibly running probes.
>   */
>  #define marker_synchronize_unregister() synchronize_sched()
>  

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