linux-kernel - Re: [PATCH] Update comment on find_task_by_pid

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Message-ID: <20100208171643.GA19230@redhat.com>
Date:	Mon, 8 Feb 2010 18:16:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] Update comment on find_task_by_pid_ns

On 02/08, Thomas Gleixner wrote:
>
> On Mon, 8 Feb 2010, Oleg Nesterov wrote:
>
> > IOW, if we change copy_process()
> >
> > 	--- kernel/fork.c
> > 	+++ kernel/fork.c
> > 	@@ -1304,8 +1304,11 @@ static struct task_struct *copy_process(
> > 		return p;
> >
> > 	 bad_fork_free_pid:
> > 	-	if (pid != &init_struct_pid)
> > 	+	if (pid != &init_struct_pid) {
> > 	+		read_lock(&tasklist_lock);
> > 			free_pid(pid);
> > 	+		read_unlock(&tasklist_lock);
> > 	+	}
> > 	 bad_fork_cleanup_io:
> > 		if (p->io_context)
> > 			exit_io_context(p);
> >
> > then find_task_by_pid_ns/etc could be used under tasklist safely even
> > with PREEMPT_RCU.
>
> We try to get rid of the read_lock sites of tasklist_lock, so please
> let's not think about adding more :)

Yes, yes, I agree. I didn't mean this patch makes sense.

Oleg.

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