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Date: Thu, 27 Nov 2008 09:36:55 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: Lai Jiangshan <laijs@...fujitsu.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, 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 On Thu, Nov 27, 2008 at 03:23:06AM +0200, Lai Jiangshan wrote: > 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@...fujitsu.com> > > Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> > > Signed-off-by: Wu Fengguang <wfg@...ux.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? Ahh, better to use "invalid data" instead of "destructed data"? > It's every good job, thank you. > > Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com> Thank you, 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. Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com> Signed-off-by: Wu Fengguang <wfg@...ux.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 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..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 + * to ensure the code and data are valid for any possibly running probes. */ #define marker_synchronize_unregister() synchronize_sched() -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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