linux-kernel - Re: [PATCH 2/5] tracepoint: Convert process iteration to use for_each_process

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Date:	Wed, 9 Apr 2014 16:28:35 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/5] tracepoint: Convert process iteration to use
 for_each_process_thread()

----- Original Message -----
> From: "Frederic Weisbecker" <fweisbec@...il.com>
> To: "LKML" <linux-kernel@...r.kernel.org>
> Cc: "Frederic Weisbecker" <fweisbec@...il.com>, "Andrew Morton" <akpm@...ux-foundation.org>, "Ingo Molnar"
> <mingo@...nel.org>, "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>, "Oleg Nesterov" <oleg@...hat.com>, "Steven
> Rostedt" <rostedt@...dmis.org>
> Sent: Wednesday, April 9, 2014 12:11:19 PM
> Subject: [PATCH 2/5] tracepoint: Convert process iteration to use for_each_process_thread()
> 
> do_each_thread/while_each_thread iterators are deprecated by
> for_each_thread/for_each_process_thread() APIs.
> 
> Lets convert the callers in the tracepoint code. The ultimate
> goal is to remove the struct task_struct::thread_group field and
> the corresponding do_each_thread/while_each_thread iterators that are
> RCU unsafe.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/tracepoint.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index fb0a38a..00a7e8b 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -561,15 +561,15 @@ static int sys_tracepoint_refcount;
>  void syscall_regfunc(void)
>  {
>  	unsigned long flags;
> -	struct task_struct *g, *t;
> +	struct task_struct *p, *t;
>  
>  	if (!sys_tracepoint_refcount) {
>  		read_lock_irqsave(&tasklist_lock, flags);
> -		do_each_thread(g, t) {
> +		for_each_process_thread(p, t) {

What are the locking rules for for_each_process_thread() ?

Is it required to hold RCU read-side lock ? (it's not the case here)

Is tasklist_lock read-side lock sufficient ?

A quick glance at those for_each iterator defines in sched.h was not
helpful in finding this information.

Thanks,

Mathieu

>  			/* Skip kernel threads. */
>  			if (t->mm)
>  				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> -		} while_each_thread(g, t);
> +		}
>  		read_unlock_irqrestore(&tasklist_lock, flags);
>  	}
>  	sys_tracepoint_refcount++;
> @@ -578,14 +578,14 @@ void syscall_regfunc(void)
>  void syscall_unregfunc(void)
>  {
>  	unsigned long flags;
> -	struct task_struct *g, *t;
> +	struct task_struct *p, *t;
>  
>  	sys_tracepoint_refcount--;
>  	if (!sys_tracepoint_refcount) {
>  		read_lock_irqsave(&tasklist_lock, flags);
> -		do_each_thread(g, t) {
> +		for_each_process_thread(p, t) {
>  			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> -		} while_each_thread(g, t);
> +		}
>  		read_unlock_irqrestore(&tasklist_lock, flags);
>  	}
>  }
> --
> 1.8.3.1
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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