[Devel] Re: [PATCH 6/15] Make alloc_pid(), free_pid() and put_pid() work with struct upid

[Pavel Emelyanov]

Oleg Nesterov wrote:
> On 07/26, Pavel Emelyanov wrote:
>> -struct pid *alloc_pid(void)
>> +struct pid *alloc_pid(struct pid_namespace *ns)
> 
> Why? We have the only caller, copy_process(), ns == task_active_pid_ns()
> always.

task_active_pid_ns() by newly created task, not the current! That's why
we need to pass something to alloc_pid() to find this new namespace.
Task or namespace itself - is the matter of choice - I selected the
most obvious argument :)

>>  {
>>  	struct pid *pid;
>>  	enum pid_type type;
>> -	int nr = -1;
>> -	struct pid_namespace *ns;
>> +	int i, nr;
>> +	struct pid_namespace *tmp;
>>  
>> -	ns = task_active_pid_ns(current);
>>  	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
>>  	if (!pid)
>>  		goto out;
>>  
>> -	nr = alloc_pidmap(ns);
>> -	if (nr < 0)
>> -		goto out_free;
>> +	tmp = ns;
>> +	for (i = ns->level; i >= 0; i--) {
>> +		nr = alloc_pidmap(tmp);
>> +		if (nr < 0)
>> +			goto out_free;
>> +
>> +		pid->numbers[i].nr = nr;
>> +		pid->numbers[i].ns = tmp;
>> +		tmp = tmp->parent;
> 
> Hm... There is no ->parent in "struct pid_namespace", and this
> patch doesn't add it.

Parent is added in another patch - 12/15. I will split it better
when sending to Andrew - patches will be smaller and bisect-safe.

>> +	if (ns != &init_pid_ns)
>> +		get_pid_ns(ns);
> 
> Q: put_pid() checks "ns != &init_pid_ns" as well, this is just
> an optimization, yes? Perhaps we can move this check into

It is :)

> get_pid_ns/put_pid_ns.

I think you're right.

> We are doing get_pid_ns() only for the "top namespace"... I guess
> this can work if pid_namespace does get_pid_ns() on its ->parent.
> This patch looks incomplete.

Yes. This set is not well split, sorry. I wanted to get comments about the
approach, bugs, etc (I have already mentioned this in another letter...)

> Oleg.
> 
> 

Thanks,
Pavel.