linux-kernel - Re: [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all allocated namespaces in the system

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Date:   Thu, 30 Jul 2020 17:12:09 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     viro@...iv.linux.org.uk, adobriyan@...il.com, davem@...emloft.net,
        ebiederm@...ssion.com, akpm@...ux-foundation.org,
        christian.brauner@...ntu.com, areber@...hat.com, serge@...lyn.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all
 allocated namespaces in the system

On 30.07.2020 16:56, Matthew Wilcox wrote:
> On Thu, Jul 30, 2020 at 04:32:22PM +0300, Kirill Tkhai wrote:
>> On 30.07.2020 15:23, Matthew Wilcox wrote:
>>> xa_erase_irqsave();
>>
>> static inline void *xa_erase_irqsave(struct xarray *xa, unsigned long index)
>> {
>> 	unsigned long flags;
>>         void *entry;
>>
>>         xa_lock_irqsave(xa, flags);
>>         entry = __xa_erase(xa, index);
>>         xa_unlock_irqrestore(xa, flags);
>>
>>         return entry;
>> }
> 
> was there a question here?

No, I just I will add this in separate patch.
 
>>>> +struct ns_common *ns_get_next(unsigned int *id)
>>>> +{
>>>> +	struct ns_common *ns;
>>>> +
>>>> +	if (*id < PROC_NS_MIN_INO - 1)
>>>> +		*id = PROC_NS_MIN_INO - 1;
>>>> +
>>>> +	*id += 1;
>>>> +	*id -= PROC_NS_MIN_INO;
>>>> +
>>>> +	rcu_read_lock();
>>>> +	do {
>>>> +		ns = idr_get_next(&ns_idr, id);
>>>> +		if (!ns)
>>>> +			break;
>>>
>>> xa_find_after();
>>>
>>> You'll want a temporary unsigned long to work with ...
>>>
>>>> +		if (!refcount_inc_not_zero(&ns->count)) {
>>>> +			ns = NULL;
>>>> +			*id += 1;
>>>
>>> you won't need this increment.
>>
>> Why? I don't see a way xarray allows to avoid this.
> 
> It's embedded in xa_find_after().
 
How is it embedded to check ns->count that it knows nothing?