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Date: Wed, 16 Jan 2013 21:35:17 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 3/3] tuntap: allow polling/writing/reading when detached
On 01/16/2013 06:59 PM, Michael S. Tsirkin wrote:
> On Wed, Jan 16, 2013 at 06:34:01PM +0800, Jason Wang wrote:
>> We forbid polling, writing and reading when the file were detached, this may
>> complex the user in several cases:
>>
>> - when guest pass some buffers to vhost/qemu and then disable some queues,
>> host/qemu needs to do its own cleanup on those buffers which is complex
>> sometimes. We can do this simply by allowing a user can still write to an
>> disabled queue. Write to an disabled queue will cause the packet pass to the
>> kernel and read will get nothing.
>> - align the polling behavior with macvtap which never fails when the queue is
>> created. This can simplify the polling errors handling of its user (e.g vhost)
>>
>> In order to achieve this, tfile->tun were not assign to NULL when detached. And
>> tfile->tun were converted to be RCU protected in order to let the data path can
>> check whether the file is deated in a lockless manner. This will be used to
>> prevent the flow caches from being updated for a detached queue.
>>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>
> NAK
>
>> ---
>> drivers/net/tun.c | 43 +++++++++++++++++++++++++------------------
>> 1 files changed, 25 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index c81680d..3f011e0 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -139,7 +139,7 @@ struct tun_file {
>> unsigned int flags;
>> u16 queue_index;
>> struct list_head next;
>> - struct tun_struct *detached;
>> + struct tun_struct __rcu *detached;
>> };
>>
>> struct tun_flow_entry {
>> @@ -295,11 +295,12 @@ static void tun_flow_cleanup(unsigned long data)
>> }
>>
>> static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
>> - u16 queue_index)
>> + struct tun_file *tfile)
>> {
>> struct hlist_head *head;
>> struct tun_flow_entry *e;
>> unsigned long delay = tun->ageing_time;
>> + u16 queue_index = tfile->queue_index;
>>
>> if (!rxhash)
>> return;
>> @@ -308,7 +309,7 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
>>
>> rcu_read_lock();
>>
>> - if (tun->numqueues == 1)
>> + if (tun->numqueues == 1 || !rtnl_dereference(tfile->detached))
>> goto unlock;
>>
>> e = tun_flow_find(head, rxhash);
> Did you try to run this with lockdep enabled?
> tun_flow_update is called from tun_get_user without rtnl so
> rtnl_dereference is arguably wrong, and will cause a lockdep warning.
Yes, will correct this and test with lockdep enabled.
Thanks
>
>> @@ -384,16 +385,16 @@ static void tun_set_real_num_queues(struct tun_struct *tun)
>>
>> static void tun_disable_queue(struct tun_struct *tun, struct tun_file *tfile)
>> {
>> - tfile->detached = tun;
>> + rcu_assign_pointer(tfile->detached, tun);
>> list_add_tail(&tfile->next, &tun->disabled);
>> ++tun->numdisabled;
>> }
>>
>> static struct tun_struct *tun_enable_queue(struct tun_file *tfile)
>> {
>> - struct tun_struct *tun = tfile->detached;
>> + struct tun_struct *tun = rtnl_dereference(tfile->detached);
>>
>> - tfile->detached = NULL;
>> + rcu_assign_pointer(tfile->detached, NULL);
>> list_del_init(&tfile->next);
>> --tun->numdisabled;
>> return tun;
>> @@ -402,26 +403,27 @@ static struct tun_struct *tun_enable_queue(struct tun_file *tfile)
>> static void __tun_detach(struct tun_file *tfile, bool clean)
>> {
>> struct tun_file *ntfile;
>> - struct tun_struct *tun;
>> + struct tun_struct *tun, *detached;
>> struct net_device *dev;
>>
>> tun = rtnl_dereference(tfile->tun);
>> + detached = rtnl_dereference(tfile->detached);
>>
>> - if (tun) {
>> + if (tun && !detached) {
>> u16 index = tfile->queue_index;
>> BUG_ON(index >= tun->numqueues);
>> dev = tun->dev;
>>
>> rcu_assign_pointer(tun->tfiles[index],
>> tun->tfiles[tun->numqueues - 1]);
>> - rcu_assign_pointer(tfile->tun, NULL);
>> ntfile = rtnl_dereference(tun->tfiles[index]);
>> ntfile->queue_index = index;
>>
>> --tun->numqueues;
>> - if (clean)
>> + if (clean) {
>> + rcu_assign_pointer(tfile->tun, NULL);
>> sock_put(&tfile->sk);
>> - else
>> + } else
>> tun_disable_queue(tun, tfile);
>>
>> synchronize_net();
>> @@ -429,7 +431,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>> /* Drop read queue */
>> skb_queue_purge(&tfile->sk.sk_receive_queue);
>> tun_set_real_num_queues(tun);
>> - } else if (tfile->detached && clean) {
>> + } else if (detached && clean) {
>> tun = tun_enable_queue(tfile);
>> sock_put(&tfile->sk);
>> }
>> @@ -466,6 +468,10 @@ static void tun_detach_all(struct net_device *dev)
>> rcu_assign_pointer(tfile->tun, NULL);
>> --tun->numqueues;
>> }
>> + list_for_each_entry(tfile, &tun->disabled, next) {
>> + wake_up_all(&tfile->wq.wait);
>> + rcu_assign_pointer(tfile->tun, NULL);
>> + }
>> BUG_ON(tun->numqueues != 0);
>>
>> synchronize_net();
>> @@ -496,7 +502,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
>> goto out;
>>
>> err = -EINVAL;
>> - if (rtnl_dereference(tfile->tun))
>> + if (rtnl_dereference(tfile->tun) && !rtnl_dereference(tfile->detached))
>> goto out;
>>
>> err = -EBUSY;
>> @@ -504,7 +510,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
>> goto out;
>>
>> err = -E2BIG;
>> - if (!tfile->detached &&
>> + if (!rtnl_dereference(tfile->detached) &&
>> tun->numqueues + tun->numdisabled == MAX_TAP_QUEUES)
>> goto out;
>>
>> @@ -521,7 +527,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
>> rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
>> tun->numqueues++;
>>
>> - if (tfile->detached)
>> + if (rtnl_dereference(tfile->detached))
>> tun_enable_queue(tfile);
>> else
>> sock_hold(&tfile->sk);
>> @@ -1195,7 +1201,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>> tun->dev->stats.rx_packets++;
>> tun->dev->stats.rx_bytes += len;
>>
>> - tun_flow_update(tun, rxhash, tfile->queue_index);
>> + tun_flow_update(tun, rxhash, tfile);
>> return total_len;
>> }
>>
>> @@ -1796,7 +1802,7 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
>> rtnl_lock();
>>
>> if (ifr->ifr_flags & IFF_ATTACH_QUEUE) {
>> - tun = tfile->detached;
>> + tun = rtnl_dereference(tfile->detached);
>> if (!tun) {
>> ret = -EINVAL;
>> goto unlock;
>> @@ -1807,7 +1813,8 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
>> ret = tun_attach(tun, file);
>> } else if (ifr->ifr_flags & IFF_DETACH_QUEUE) {
>> tun = rtnl_dereference(tfile->tun);
>> - if (!tun || !(tun->flags & TUN_TAP_MQ))
>> + if (!tun || !(tun->flags & TUN_TAP_MQ) ||
>> + rtnl_dereference(tfile->detached))
>> ret = -EINVAL;
>> else
>> __tun_detach(tfile, false);
>> --
>> 1.7.1
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