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From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: viro@zeniv.linux.org.uk, adobriyan@gmail.com,
	davem@davemloft.net, ebiederm@xmission.com,
	akpm@linux-foundation.org, christian.brauner@ubuntu.com,
	areber@redhat.com, serge@hallyn.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all allocated namespaces in the system
Date: Thu, 30 Jul 2020 16:32:22 +0300
Message-ID: <485c01e6-a4ee-5076-878e-6303e6d8d5f3@virtuozzo.com> (raw)
In-Reply-To: <20200730122319.GC23808@casper.infradead.org>

On 30.07.2020 15:23, Matthew Wilcox wrote:
> On Thu, Jul 30, 2020 at 03:00:08PM +0300, Kirill Tkhai wrote:
>> This patch introduces a new IDR and functions to add/remove and iterate
>> registered namespaces in the system. It will be used to list namespaces
>> in /proc/namespaces/... in next patches.
> 
> Looks like you could use an XArray for this and it would be fewer lines of
> code.
> 
>>  
>>  static struct vfsmount *nsfs_mnt;
>> +static DEFINE_SPINLOCK(ns_lock);
>> +static DEFINE_IDR(ns_idr);
> 
> XArray includes its own spinlock.
> 
>> +/*
>> + * Add a newly created ns to ns_idr. The ns must be fully
>> + * initialized since it becomes available for ns_get_next()
>> + * right after we exit this function.
>> + */
>> +int ns_idr_register(struct ns_common *ns)
>> +{
>> +	int ret, id = ns->inum - PROC_NS_MIN_INO;
>> +
>> +	if (WARN_ON(id < 0))
>> +		return -EINVAL;
>> +
>> +	idr_preload(GFP_KERNEL);
>> +	spin_lock_irq(&ns_lock);
>> +	ret = idr_alloc(&ns_idr, ns, id, id + 1, GFP_ATOMIC);
>> +	spin_unlock_irq(&ns_lock);
>> +	idr_preload_end();
>> +	return ret < 0 ? ret : 0;
> 
> This would simply be return xa_insert_irq(...);
> 
>> +}
>> +
>> +/*
>> + * Remove a dead ns from ns_idr. Note, that ns memory must
>> + * be freed not earlier then one RCU grace period after
>> + * this function, since ns_get_next() uses RCU to iterate the IDR.
>> + */
>> +void ns_idr_unregister(struct ns_common *ns)
>> +{
>> +	int id = ns->inum - PROC_NS_MIN_INO;
>> +	unsigned long flags;
>> +
>> +	if (WARN_ON(id < 0))
>> +		return;
>> +
>> +	spin_lock_irqsave(&ns_lock, flags);
>> +	idr_remove(&ns_idr, id);
>> +	spin_unlock_irqrestore(&ns_lock, flags);
>> +}
> 
> 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;
}

>> +
>> +/*
>> + * This returns ns with inum greater than @id or NULL.
>> + * @id is updated to refer the ns inum.
>> + */
>> +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.

  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-30 11:59 [PATCH 00/23] proc: Introduce /proc/namespaces/ directory to expose namespaces lineary Kirill Tkhai
2020-07-30 11:59 ` [PATCH 01/23] ns: Add common refcount into ns_common add use it as counter for net_ns Kirill Tkhai
2020-07-30 13:35   ` Christian Brauner
2020-07-30 14:07     ` Kirill Tkhai
2020-07-30 15:59       ` Christian Brauner
2020-07-30 14:30   ` Christian Brauner
2020-07-30 14:34     ` Kirill Tkhai
2020-07-30 14:39       ` Christian Brauner
2020-07-30 11:59 ` [PATCH 02/23] uts: Use generic ns_common::count Kirill Tkhai
2020-07-30 14:30   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 03/23] ipc: " Kirill Tkhai
2020-07-30 14:32   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 04/23] pid: " Kirill Tkhai
2020-07-30 14:37   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 05/23] user: " Kirill Tkhai
2020-07-30 14:46   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 06/23] mnt: " Kirill Tkhai
2020-07-30 14:49   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 07/23] cgroup: " Kirill Tkhai
2020-07-30 14:50   ` Christian Brauner
2020-07-30 12:00 ` [PATCH 08/23] time: " Kirill Tkhai
2020-07-30 14:52   ` Christian Brauner
2020-07-30 12:00 ` [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all allocated namespaces in the system Kirill Tkhai
2020-07-30 12:23   ` Matthew Wilcox
2020-07-30 13:32     ` Kirill Tkhai [this message]
2020-07-30 13:56       ` Matthew Wilcox
2020-07-30 14:12         ` Kirill Tkhai
2020-07-30 14:15           ` Matthew Wilcox
2020-07-30 14:20             ` Kirill Tkhai
2020-07-30 12:00 ` [PATCH 10/23] fs: Rename fs/proc/namespaces.c into fs/proc/task_namespaces.c Kirill Tkhai
2020-07-30 12:00 ` [PATCH 11/23] fs: Add /proc/namespaces/ directory Kirill Tkhai
2020-07-30 12:18   ` Alexey Dobriyan
2020-07-30 13:22     ` Kirill Tkhai
2020-07-30 13:26   ` Christian Brauner
2020-07-30 14:30     ` Kirill Tkhai
2020-07-30 20:47   ` kernel test robot
2020-07-30 22:20   ` kernel test robot
2020-08-05  8:17   ` kernel test robot
2020-08-05  8:17   ` [RFC PATCH] fs: namespaces_dentry_operations can be static kernel test robot
2020-07-30 12:00 ` [PATCH 12/23] user: Free user_ns one RCU grace period after final counter put Kirill Tkhai
2020-07-30 12:00 ` [PATCH 13/23] user: Add user namespaces into ns_idr Kirill Tkhai
2020-07-30 12:00 ` [PATCH 14/23] net: Add net " Kirill Tkhai
2020-07-30 12:00 ` [PATCH 15/23] pid: Eextract child_reaper check from pidns_for_children_get() Kirill Tkhai
2020-07-30 12:00 ` [PATCH 16/23] proc_ns_operations: Add can_get method Kirill Tkhai
2020-07-30 12:00 ` [PATCH 17/23] pid: Add pid namespaces into ns_idr Kirill Tkhai
2020-07-30 12:00 ` [PATCH 18/23] uts: Free uts namespace one RCU grace period after final counter put Kirill Tkhai
2020-07-30 12:01 ` [PATCH 19/23] uts: Add uts namespaces into ns_idr Kirill Tkhai
2020-07-30 12:01 ` [PATCH 20/23] ipc: Add ipc " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 21/23] mnt: Add mount " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 22/23] cgroup: Add cgroup " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 23/23] time: Add time " Kirill Tkhai
2020-07-30 13:08 ` [PATCH 00/23] proc: Introduce /proc/namespaces/ directory to expose namespaces lineary Christian Brauner
2020-07-30 13:38   ` Christian Brauner
2020-07-30 14:34 ` Eric W. Biederman
2020-07-30 14:42   ` Christian Brauner
2020-07-30 15:01   ` Kirill Tkhai
2020-07-30 22:13     ` Eric W. Biederman
2020-07-31  8:48       ` Pavel Tikhomirov
2020-08-03 10:03       ` Kirill Tkhai
2020-08-03 10:51         ` Alexey Dobriyan
2020-08-06  8:05         ` Andrei Vagin
2020-08-07  8:47           ` Kirill Tkhai
2020-08-10 17:34             ` Andrei Vagin
2020-08-11 10:23               ` Kirill Tkhai
2020-08-12 17:53                 ` Andrei Vagin
2020-08-13  8:12                   ` Kirill Tkhai
2020-08-14  1:16                     ` Andrei Vagin
2020-08-14 15:11                       ` Kirill Tkhai
2020-08-14 19:21                         ` Andrei Vagin
2020-08-17 14:05                           ` Kirill Tkhai
2020-08-17 15:48                             ` Eric W. Biederman
2020-08-17 17:47                               ` Christian Brauner
2020-08-17 18:53                                 ` Eric W. Biederman
2020-08-04  5:43     ` Andrei Vagin
2020-08-04 12:11       ` Pavel Tikhomirov
2020-08-04 14:47       ` Kirill Tkhai

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