linux-kernel - Re: [RFC PATCH] Kernel Tracepoints (update)

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Date:	Thu, 03 Jul 2008 14:46:37 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
	"'Alexey Dobriyan'" <adobriyan@...il.com>,
	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'Steven Rostedt'" <rostedt@...dmis.org>,
	"'Frank Ch. Eigler'" <fche@...hat.com>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'LKML'" <linux-kernel@...r.kernel.org>,
	"'systemtap-ml'" <systemtap@...rces.redhat.com>,
	"'Hideo AOKI'" <haoki@...hat.com>
Subject: Re: [RFC PATCH] Kernel Tracepoints (update)

Hi Mathieu,

Mathieu Desnoyers wrote:
> Hi Masami,
> 
> I am thinking about removing the private_data, because such declaration
> won't work :
> 
> DEFINE_TRACE(kernel_irq_exit,
>         TPPROTO(void),
>         TPARGS());
> 
> because the arguments become :
> 
> (void *private_data, void)

Oh, you right.
since there is no tracepoint user who uses private_data,
we can remove it.

> Any better idea ?

If you need it, I think you can introduce some macros like below.

#define TPPROTO(args...) (void *private_data, args)

#define __define_trace_register(name, proto) \ /*shared by DEFINE_TRACE/DEFINE_TRACE_NOARG*/
	static inline int register_trace_##name(\
		void (*probe)proto,		\
		void *private_data)		\
	{								\
		return tracepoint_probe_register(#name ":" #proto,	\
			(void *)probe, private_data);			\
	}								\
	static inline void unregister_trace_##name(			\
		void (*probe)proto,		\
		void *private_data)					\
	{								\
		tracepoint_probe_unregister(#name ":" #proto,		\
			(void *)probe, private_data);			\
	}

#define DEFINE_TRACE_NOARG(name) \
 static inline void _do_trace_##name(struct tracepoint *tp) \
 ...
 static inline void trace_##name(void)			\
 ...
 __define_trace_register(name, (void *private_data))


But I think removing private_data is better...

Thank you,

> 
> Mathieu
> 
> * Masami Hiramatsu (mhiramat@...hat.com) wrote:
>> Hi Mathieu,
>>
>> I found a bug.
>> Mathieu Desnoyers wrote:
>> [...]
>>
>>> +/*
>>> + * Remove the tracepoint from the tracepoint hash table. Must be called with
>>> + * mutex_lock held.
>>> + */
>>> +static int remove_tracepoint(const char *name)
>>> +{
>>> +	struct hlist_head *head;
>>> +	struct hlist_node *node;
>>> +	struct tracepoint_entry *e;
>>> +	int found = 0;
>>> +	size_t len = strlen(name) + 1;
>>> +	u32 hash = jhash(name, len-1, 0);
>>> +
>>> +	head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
>>> +	hlist_for_each_entry(e, node, head, hlist) {
>>> +		if (!strcmp(name, e->name)) {
>>> +			found = 1;
>>> +			break;
>>> +		}
>>> +	}
>>> +	if (!found)
>>> +		return -ENOENT;
>> before removing, you have to ensure refcount == 0. So,
>> 	if (e->refcount != 0)
>> 		return -EBUSY;
>>
>>> +	hlist_del(&e->hlist);
>>> +	/* Make sure the call_rcu has been executed */
>>> +	if (e->rcu_pending)
>>> +		rcu_barrier();
>>> +	kfree(e);
>>> +	return 0;
>>> +}
>> Thank you,
>>
>> -- 
>> Masami Hiramatsu
>>
>> Software Engineer
>> Hitachi Computer Products (America) Inc.
>> Software Solutions Division
>>
>> e-mail: mhiramat@...hat.com
>>
> 

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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