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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Message-ID: <20200730135640.GE23808@casper.infradead.org>
Date:   Thu, 30 Jul 2020 14:56:40 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
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 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?

> >> +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().