Re: [PATCH 01/24] pidns: Remove races by stopping the caching of proc_mnt

["Serge E. Hallyn" <serge@hallyn.com>]

Quoting Eric W. Biederman (ebiederm@xmission.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