linux-kernel - Re: [PATCH 01/24] pidns: Remove races by stopping the caching of proc

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Message-ID: <20100709221341.GA31259@hallyn.com>
Date:	Fri, 9 Jul 2010 17:13:41 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH 01/24] pidns: Remove races by stopping the caching of
 proc_mnt

Quoting Eric W. Biederman (ebiederm@...ssion.com):
...
> @@ -2742,13 +2743,13 @@ void proc_flush_task(struct task_struct *task)
>  
>  	for (i = 0; i <= pid->level; i++) {
>  		upid = &pid->numbers[i];
> -		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
> -					tgid->numbers[i].nr);
> -	}
> +		mnt = get_proc_mnt(upid->ns);

...

> -int pid_ns_prepare_proc(struct pid_namespace *ns)
> +struct vfsmount *get_proc_mnt(struct pid_namespace *ns)
>  {
> -	struct vfsmount *mnt;
> -
> -	mnt = kern_mount_data(&proc_fs_type, ns);
> -	if (IS_ERR(mnt))
> -		return PTR_ERR(mnt);
> -
> -	return 0;
> +	return kern_mount_data(&proc_fs_type, ns);

Uh, that looks like it's got to be a *huge* hit.  Each kern_mount_data()
will at least alloc space for a vfsmnt and proc_fs_type->name.  Once for
each pid level of each exiting task.

(Or am I misreading?)

-serge
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