Date: Tue, 14 Dec 2010 17:04:21 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: "Suzuki K. Poulose" <suzuki@in.ibm.com>
Cc: linux-kernel@vger.kernel.org,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Christoph Hellwig <hch@lst.de>, Masami Hiramatsu <mhiramat@redhat.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Daisuke HATAYAMA <d.hatayama@jp.fujitsu.com>,
        Andi Kleen <andi@firstfloor.org>, Roland McGrath <roland@redhat.com>,
        Amerigo Wang <amwang@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [Patch 11/21] Track the core generation requests
Message-ID: <20101214160421.GD11400@redhat.com>
References: <20101214152259.67896960@suzukikp> <20101214154204.21048247@suzukikp>
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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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