linux-kernel - Re: [tip:tracing/urgent] tracing: Allocate the ftrace event profile buffer dynamically

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Message-Id: <1253367914.20020.338.camel@gandalf.stny.rr.com>
Date:	Sat, 19 Sep 2009 09:45:14 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	lizf@...fujitsu.com, peterz@...radead.org, fweisbec@...il.com,
	tglx@...utronix.de, jbaron@...hat.com, mhiramat@...hat.com,
	mingo@...e.hu
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:tracing/urgent] tracing: Allocate the ftrace event
 profile buffer dynamically

On Sat, 2009-09-19 at 07:58 +0000, tip-bot for Frederic Weisbecker
wrote:

> +/*
> + * We can't use a size but a type in alloc_percpu()
> + * So let's create a dummy type that matches the desired size
> + */
> +typedef struct {char buf[FTRACE_MAX_PROFILE_SIZE];} profile_buf_t;
> +
>  static int ftrace_profile_enable_event(struct ftrace_event_call *event)
>  {
> +	char *buf;
> +	int ret;
> +
>  	if (atomic_inc_return(&event->profile_count))
>  		return 0;
>  
> -	return event->profile_enable();
> +	buf = (char *)alloc_percpu(profile_buf_t);
> +	if (!buf)
> +		return -ENOMEM;

Ingo,

Did you pull in the version that allocates a buffer for each event? I
thought Frederic made just a global per cpu buffer that all events can
use. The buffer is just a temporary storage that will be too big to put
on the stack.

-- Steve

> +
> +	rcu_assign_pointer(event->profile_buf, buf);
> +
> +	buf = (char *)alloc_percpu(profile_buf_t);
> +	if (!buf) {
> +		ret = -ENOMEM;
> +		goto fail_nmi;
> +	}
> +
> +	rcu_assign_pointer(event->profile_buf_nmi, buf);
> +
> +	ret = event->profile_enable();
> +	if (!ret)
> +		return 0;
> +
> +	kfree(event->profile_buf_nmi);
> +fail_nmi:
> +	kfree(event->profile_buf);
> +
> +	return ret;
>  }
>  

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