linux-kernel - Re: [PATCH v3 2/4] tracing/user_events: Introduce multi-format events

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Message-ID: <20240221165613.GB441-beaub@linux.microsoft.com>
Date: Wed, 21 Feb 2024 08:56:13 -0800
From: Beau Belgrave <beaub@...ux.microsoft.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: mhiramat@...nel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com
Subject: Re: [PATCH v3 2/4] tracing/user_events: Introduce multi-format events

On Wed, Feb 21, 2024 at 10:08:33AM -0500, Steven Rostedt wrote:
> On Wed, 14 Feb 2024 17:50:44 +0000
> Beau Belgrave <beaub@...ux.microsoft.com> wrote:
> 
> > +static char *user_event_group_system_multi_name(void)
> > +{
> > +	char *system_name;
> > +	int len = sizeof(USER_EVENTS_MULTI_SYSTEM) + 1;
> 
> FYI, the sizeof() will include the "\0" so no need for "+ 1", but I don't
> think this matters as for what I mention below.
> 
> > +
> > +	system_name = kmalloc(len, GFP_KERNEL);
> > +
> > +	if (!system_name)
> > +		return NULL;
> > +
> > +	snprintf(system_name, len, "%s", USER_EVENTS_MULTI_SYSTEM);
> > +
> > +	return system_name;
> 
> Hmm, the above looks like an open coded version of:
> 
> 	system_name = kstrdup(USER_EVENTS_MULTI_SYSTEM, GFP_KERNEL);
> 

That's much cleaner, I'll move to that.

> 
> > +}
> > +
> >  static struct user_event_group *current_user_event_group(void)
> >  {
> >  	return init_group;
> > @@ -367,6 +390,11 @@ static struct user_event_group *user_event_group_create(void)
> >  	if (!group->system_name)
> >  		goto error;
> >  
> > +	group->system_multi_name = user_event_group_system_multi_name();
> > +
> > +	if (!group->system_multi_name)
> > +		goto error;
> > +
> >  	mutex_init(&group->reg_mutex);
> >  	hash_init(group->register_table);
> >  
> > @@ -1482,6 +1510,11 @@ static int destroy_user_event(struct user_event *user)
> >  	hash_del(&user->node);
> >  
> >  	user_event_destroy_validators(user);
> > +
> > +	/* If we have different names, both must be freed */
> > +	if (EVENT_NAME(user) != EVENT_TP_NAME(user))
> > +		kfree(EVENT_TP_NAME(user));
> > +
> >  	kfree(user->call.print_fmt);
> >  	kfree(EVENT_NAME(user));
> >  	kfree(user);
> > @@ -1504,12 +1537,24 @@ static struct user_event *find_user_event(struct user_event_group *group,
> >  	*outkey = key;
> >  
> >  	hash_for_each_possible(group->register_table, user, node, key) {
> > +		/*
> > +		 * Single-format events shouldn't return multi-format
> > +		 * events. Callers expect the underlying tracepoint to match
> > +		 * the name exactly in these cases. Only check like-formats.
> > +		 */
> > +		if (EVENT_MULTI_FORMAT(flags) != EVENT_MULTI_FORMAT(user->reg_flags))
> > +			continue;
> > +
> >  		if (strcmp(EVENT_NAME(user), name))
> >  			continue;
> >  
> >  		if (user_fields_match(user, argc, argv))
> >  			return user_event_get(user);
> >  
> > +		/* Scan others if this is a multi-format event */
> > +		if (EVENT_MULTI_FORMAT(flags))
> > +			continue;
> > +
> >  		return ERR_PTR(-EADDRINUSE);
> >  	}
> >  
> > @@ -1889,8 +1934,12 @@ static bool user_event_match(const char *system, const char *event,
> >  	struct user_event *user = container_of(ev, struct user_event, devent);
> >  	bool match;
> >  
> > -	match = strcmp(EVENT_NAME(user), event) == 0 &&
> > -		(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
> > +	match = strcmp(EVENT_NAME(user), event) == 0;
> > +
> > +	if (match && system) {
> > +		match = strcmp(system, user->group->system_name) == 0 ||
> > +			strcmp(system, user->group->system_multi_name) == 0;
> > +	}
> >  
> >  	if (match)
> >  		match = user_fields_match(user, argc, argv);
> > @@ -1923,6 +1972,39 @@ static int user_event_trace_register(struct user_event *user)
> >  	return ret;
> >  }
> >  
> > +static int user_event_set_tp_name(struct user_event *user)
> > +{
> > +	lockdep_assert_held(&user->group->reg_mutex);
> > +
> > +	if (EVENT_MULTI_FORMAT(user->reg_flags)) {
> > +		char *multi_name;
> > +		int len;
> > +
> > +		len = snprintf(NULL, 0, "%s.%llx", user->reg_name,
> > +			       user->group->multi_id) + 1;
> > +
> > +		multi_name = kzalloc(len, GFP_KERNEL_ACCOUNT);
> > +
> > +		if (!multi_name)
> > +			return -ENOMEM;
> > +
> > +		snprintf(multi_name, len, "%s.%llx", user->reg_name,
> > +			 user->group->multi_id);
> 
> I believe the above can be replaced with:
> 
> 		multi_name = kasprintf(GFP_KERNEL_ACCOUNT, "%s.%llx", user->reg_name,
> 				       user->group->multi_id);
> 		if (!multi_name)
> 			return -ENOMEM;
> 

Great, I'll move to that as well and validate.

Thanks,
-Beau

> -- Steve
> 
> > +
> > +		user->call.name = multi_name;
> > +		user->tracepoint.name = multi_name;
> > +
> > +		/* Inc to ensure unique multi-event name next time */
> > +		user->group->multi_id++;
> > +	} else {
> > +		/* Non Multi-format uses register name */
> > +		user->call.name = user->reg_name;
> > +		user->tracepoint.name = user->reg_name;
> > +	}
> > +
> > +	return 0;
> > +}