linux-kernel - Re: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task other than ourself

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Date:	Thu, 23 Jul 2009 11:33:20 -0400
From:	Oren Laadan <orenl@...rato.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Dave Hansen <dave@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Oren Laadan <orenl@...columbia.edu>
Subject: Re: [RFC v17][PATCH 22/60] c/r: external checkpoint of a task	other
 than ourself



Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl@...rato.com):
>> +/* setup checkpoint-specific parts of ctx */
>> +static int init_checkpoint_ctx(struct ckpt_ctx *ctx, pid_t pid)
>> +{
>> +	struct task_struct *task;
>> +	struct nsproxy *nsproxy;
>> +	int ret;
>> +
>> +	/*
>> +	 * No need for explicit cleanup here, because if an error
>> +	 * occurs then ckpt_ctx_free() is eventually called.
>> +	 */
>> +
>> +	ctx->root_pid = pid;
>> +
>> +	/* root task */
>> +	read_lock(&tasklist_lock);
>> +	task = find_task_by_vpid(pid);
>> +	if (task)
>> +		get_task_struct(task);
>> +	read_unlock(&tasklist_lock);
>> +	if (!task)
>> +		return -ESRCH;
>> +	else
>> +		ctx->root_task = task;
>> +
>> +	/* root nsproxy */
>> +	rcu_read_lock();
>> +	nsproxy = task_nsproxy(task);
>> +	if (nsproxy)
>> +		get_nsproxy(nsproxy);
>> +	rcu_read_unlock();
>> +	if (!nsproxy)
>> +		return -ESRCH;
>> +	else
>> +		ctx->root_nsproxy = nsproxy;
>> +
>> +	/* root freezer */
>> +	ctx->root_freezer = task;
>> +	geT_task_struct(task);
>> +
>> +	ret = may_checkpoint_task(ctx, task);
>> +	if (ret) {
>> +		ckpt_write_err(ctx, NULL);
>> +		put_task_struct(task);
>> +		put_task_struct(task);
>> +		put_nsproxy(nsproxy);
> 
> I don't think this is safe - the ckpt_ctx_free() will
> free them a second time because you're not setting them
> to NULL, right?

Yes. Fortunately this hole chunk is removed by the 3rd-next patch.
I'll make sure it's correct here too.

Thanks,

Oren.

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