linux-kernel - Re: [PATCH 4/7] add syscall tracepoints

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Date:	Fri, 19 Jun 2009 16:31:09 +0800
From:	Li Zefan <lizf@...fujitsu.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,
	bligh@...gle.com, roland@...hat.com, fche@...hat.com
Subject: Re: [PATCH 4/7] add syscall tracepoints

>  /*
>   * A syscall entry in the ftrace syscalls array.
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 1ef5d3a..5b34ff9 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -24,6 +24,7 @@
>  #include <linux/tracepoint.h>
>  #include <linux/err.h>
>  #include <linux/slab.h>
> +#include <linux/sched.h>
>  
>  extern struct tracepoint __start___tracepoints[];
>  extern struct tracepoint __stop___tracepoints[];
> @@ -577,3 +578,40 @@ static int init_tracepoints(void)
>  __initcall(init_tracepoints);
>  
>  #endif /* CONFIG_MODULES */
> +
> +DEFINE_MUTEX(regfunc_mutex);

static?

> +int sys_tracepoint_refcount;

static?

and atomic_t should be fine as Frederic pointed out.

> +
> +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) {
> +			set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +		} while_each_thread(g, t);
> +		read_unlock_irqrestore(&tasklist_lock, flags);
> +	}
> +	sys_tracepoint_refcount++;
> +	mutex_unlock(&regfunc_mutex);
> +}
> +
> +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);
> +		do_each_thread(g, t) {
> +			clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +		} while_each_thread(g, t);
> +		read_unlock_irqrestore(&tasklist_lock, flags);
> +	}
> +	mutex_unlock(&regfunc_mutex);
> +}

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