linux-kernel - Re: [PATCH] Make /proc/net a symlink on /proc/self/net

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Message-ID: <20080306002205.GI8728@linux.vnet.ibm.com>
Date:	Wed, 5 Mar 2008 16:22:05 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...nvz.org>
Subject: Re: [PATCH] Make /proc/net a symlink on /proc/self/net

On Wed, Mar 05, 2008 at 04:59:56PM -0700, Eric W. Biederman wrote:
> >> 
> >> +static struct net *get_proc_task_net(struct inode *dir)
> >> +{
> >> +	struct task_struct *task;
> >> +	struct nsproxy *ns;
> >> +	struct net *net = NULL;
> >> +
> >> +	rcu_read_lock();
> >> +	task = get_proc_task(dir);
> >
> > This implies a get_task_struct(), as get_proc_task() invokes get_proc_task()
> > which invokes get_pid_task() which invokes get_task_struct().
> >
> > I don't see the corresponding put_task_struct() -- what am I missing here?
> 
> You aren't.  However we can easily make this:
> 	task = pid_task(proc_pid(dir), PIDTYPE_PID);
> And we won't need to increment the count on the task_struct.

That looks like it should do the trick!  And the net_get() below
will allow you to safely export the "net" pointer out of an RCU
read-side critical section, so with that change looks good to me!

						Thanx, Paul

> Good catch.
> 
> >> +	if (task != NULL) {
> >> +		ns = task_nsproxy(task);
> >> +		if (ns != NULL)
> >> +			net = get_net(ns->net_ns);
> >> +	}
> >> +	rcu_read_unlock();
> >> +
> >> +	return net;
> >> +}
> >> +
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