linux-kernel - Re: [PATCH] tracing/profile: Fix profile_disable vs module

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Date:	Wed, 26 Aug 2009 14:01:14 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> This patch solves the problem that Li originally reported. If something 
> registers a trace point belonging to a module, then it ups the ref count 
> of the module. This prevents a process from registering a probe to a 
> tracepoint belonging to a module and then having the module disappear.
> 
> Doing the example with perf in Li's original post, now errors on the 
> rmmod, with "ERROR: Module trace_events_sample is in use".
> 
> Mathieu, can I have your acked-by on this?
> 

Sorry, it looks buggy.

It does not deal with the fact that tracepoints with the same name and
arguments can be present in more than one module, or in a combination of
kernel core and modules.

The struct tracepoint_entry is specific to a a tracepoint name, used for
registration, but is eventually tied to all tracepoint instrumentation
instances for this tracepoint name.

Mathieu

> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 0341f2e..055275b 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -109,8 +109,9 @@ struct tracepoint {
>  #define EXPORT_TRACEPOINT_SYMBOL(name)					\
>  	EXPORT_SYMBOL(__tracepoint_##name)
>  
> -extern void tracepoint_update_probe_range(struct tracepoint *begin,
> -	struct tracepoint *end);
> +extern void tracepoint_update_probe_range(struct module *,
> +					  struct tracepoint *begin,
> +					  struct tracepoint *end);
>  
>  #else /* !CONFIG_TRACEPOINTS */
>  #define DECLARE_TRACE_WITH_CALLBACK(name, proto, args, reg, unreg)	\
> diff --git a/kernel/module.c b/kernel/module.c
> index b182143..a8e69fa 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2974,7 +2974,7 @@ void module_update_tracepoints(void)
>  	mutex_lock(&module_mutex);
>  	list_for_each_entry(mod, &modules, list)
>  		if (!mod->taints)
> -			tracepoint_update_probe_range(mod->tracepoints,
> +			tracepoint_update_probe_range(mod, mod->tracepoints,
>  				mod->tracepoints + mod->num_tracepoints);
>  	mutex_unlock(&module_mutex);
>  }
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 06f165a..089e6f9 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -54,6 +54,7 @@ static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
>   */
>  struct tracepoint_entry {
>  	struct hlist_node hlist;
> +	struct module *mod;
>  	void **funcs;
>  	int refcount;	/* Number of times armed. 0 if disarmed. */
>  	char name[0];
> @@ -221,6 +222,7 @@ static struct tracepoint_entry *add_tracepoint(const char *name)
>  	memcpy(&e->name[0], name, name_len);
>  	e->funcs = NULL;
>  	e->refcount = 0;
> +	e->mod = NULL;	/* Will be assigned in tracepoint_update_probe_range */
>  	hlist_add_head(&e->hlist, head);
>  	return e;
>  }
> @@ -231,6 +233,8 @@ static struct tracepoint_entry *add_tracepoint(const char *name)
>   */
>  static inline void remove_tracepoint(struct tracepoint_entry *e)
>  {
> +	if (e->mod)
> +		module_put(e->mod);
>  	hlist_del(&e->hlist);
>  	kfree(e);
>  }
> @@ -274,7 +278,8 @@ static void disable_tracepoint(struct tracepoint *elem)
>   * Updates the probe callback corresponding to a range of tracepoints.
>   */
>  void
> -tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
> +tracepoint_update_probe_range(struct module *mod,
> +			      struct tracepoint *begin, struct tracepoint *end)
>  {
>  	struct tracepoint *iter;
>  	struct tracepoint_entry *mark_entry;
> @@ -286,9 +291,15 @@ tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
>  	for (iter = begin; iter < end; iter++) {
>  		mark_entry = get_tracepoint(iter->name);
>  		if (mark_entry) {
> +			if (mod && !mark_entry->mod) {
> +				if (!try_module_get(mod))
> +					goto disable;
> +				mark_entry->mod = mod;
> +			}
>  			set_tracepoint(&mark_entry, iter,
>  					!!mark_entry->refcount);
>  		} else {
> + disable:
>  			disable_tracepoint(iter);
>  		}
>  	}
> @@ -301,7 +312,7 @@ tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
>  static void tracepoint_update_probes(void)
>  {
>  	/* Core kernel tracepoints */
> -	tracepoint_update_probe_range(__start___tracepoints,
> +	tracepoint_update_probe_range(NULL, __start___tracepoints,
>  		__stop___tracepoints);
>  	/* tracepoints in modules. */
>  	module_update_tracepoints();
> @@ -556,7 +567,7 @@ int tracepoint_module_notify(struct notifier_block *self,
>  	switch (val) {
>  	case MODULE_STATE_COMING:
>  	case MODULE_STATE_GOING:
> -		tracepoint_update_probe_range(mod->tracepoints,
> +		tracepoint_update_probe_range(mod, mod->tracepoints,
>  			mod->tracepoints + mod->num_tracepoints);
>  		break;
>  	}
> 
> 

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