linux-kernel - Re: [Patch 11/21] Track the core generation requests

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Date:	Tue, 14 Dec 2010 17:04:21 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Suzuki K. Poulose" <suzuki@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Christoph Hellwig <hch@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Daisuke HATAYAMA <d.hatayama@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Amerigo Wang <amwang@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch 11/21] Track the core generation requests

On 12/14, Suzuki K. Poulose wrote:
>
> Concurrent core generation requests
> for the same target process are not allowed.

OK, but

> +static struct core_proc* get_core_proc(struct task_struct *t)
> +{
> +	struct core_proc *cp;
> +
> +	list_for_each_entry(cp, &core_list, list) {
> +		if (cp->task == t->group_leader)
> +			return cp;
> +	}
> +	return NULL;
> +}
> ...
>  static int open_gencore(struct inode *inode, struct file *filp)
>  {
> -	return 0;
> +	struct task_struct *task = get_proc_task(inode);
> +	struct core_proc *cp;
> +	int ret = 0;
> +
> +	if (!task)
> +		return -ENOENT;
> +
> +	mutex_lock(&core_mutex);
> +	cp = get_core_proc(task);
> +	if (cp) {
> +		ret = -EALREADY;

I don't think this can work.

The task can change ->group_leader. This means 2 or more
open_gencore() can succeed if this task execs in between.

Oleg.

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