linux-kernel - Re: [PATCH] tracing: Move tracepoint callbacks into DEFINE

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Date:	Thu, 20 Aug 2009 10:25:59 -0700
From:	Josh Stone <jistone@...hat.com>
To:	Jason Baron <jbaron@...hat.com>
CC:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...e.hu,
	laijs@...fujitsu.com, rostedt@...dmis.org, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	mbligh@...gle.com, lizf@...fujitsu.com
Subject: Re: [PATCH] tracing: Move tracepoint callbacks into DEFINE

On 08/19/2009 09:13 AM, Jason Baron wrote:
> On Tue, Aug 18, 2009 at 12:23:47AM -0700, Josh Stone wrote:
>> --- a/kernel/tracepoint.c
>> +++ b/kernel/tracepoint.c
>> @@ -243,6 +243,11 @@ static void set_tracepoint(struct tracepoint_entry **entry,
>>  {
>>  	WARN_ON(strcmp((*entry)->name, elem->name) != 0);
>>  
>> +	if (elem->regfunc && !elem->state && active)
>> +		elem->regfunc();
>> +	else if (elem->unregfunc && elem->state && !active)
>> +		elem->unregfunc();
>> +
>>  	/*
>>  	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
>>  	 * probe callbacks array is consistent before setting a pointer to it.
>> @@ -262,6 +267,9 @@ static void set_tracepoint(struct tracepoint_entry **entry,
>>   */
>>  static void disable_tracepoint(struct tracepoint *elem)
>>  {
>> +	if (elem->unregfunc && elem->state)
>> +		elem->unregfunc();
>> +
>>  	elem->state = 0;
>>  	rcu_assign_pointer(elem->funcs, NULL);
>>  }
>> @@ -581,15 +589,13 @@ __initcall(init_tracepoints);
>>  
>>  #ifdef CONFIG_FTRACE_SYSCALLS
>>  
>> -static DEFINE_MUTEX(regfunc_mutex);
>> -static int sys_tracepoint_refcount;
>> +static int sys_tracepoint_refcount; /* guarded by tracepoints_mutex */
>>  
>>  void syscall_regfunc(void)
>>  {
>>  	unsigned long flags;
>>  	struct task_struct *g, *t;
>>  
>> -	mutex_lock(&regfunc_mutex);
>>  	if (!sys_tracepoint_refcount) {
>>  		read_lock_irqsave(&tasklist_lock, flags);
>>  		do_each_thread(g, t) {
>> @@ -598,7 +604,6 @@ void syscall_regfunc(void)
>>  		read_unlock_irqrestore(&tasklist_lock, flags);
>>  	}
>>  	sys_tracepoint_refcount++;
>> -	mutex_unlock(&regfunc_mutex);
>>  }
>>  
>>  void syscall_unregfunc(void)
>> @@ -606,7 +611,6 @@ void syscall_unregfunc(void)
>>  	unsigned long flags;
>>  	struct task_struct *g, *t;
>>  
>> -	mutex_lock(&regfunc_mutex);
>>  	sys_tracepoint_refcount--;
>>  	if (!sys_tracepoint_refcount) {
>>  		read_lock_irqsave(&tasklist_lock, flags);
>> @@ -615,6 +619,5 @@ void syscall_unregfunc(void)
>>  		} while_each_thread(g, t);
>>  		read_unlock_irqrestore(&tasklist_lock, flags);
>>  	}
>> -	mutex_unlock(&regfunc_mutex);
>>  }
>>  #endif
> 
> if we disable,  CONFIG_FTRACE_SYSCALLS, then we get undefined references
> to syscall_regfunc, and syscall_unregfunc. So, i think we just need to
> remove the 'CONFIG_FTRACE_SYSCALLS' ifdef here.

This CONFIG check was added by commit 60d970c2 to deal with missing
TIF_SYSCALL_FTRACE.  Perhaps the functions should just have their bodies
#ifdef'ed?

Josh
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