On 2019/9/2 13:32, Jason Wang wrote:
On 2019/8/23 下午5:36, Yang Yingliang wrote:
On 2019/8/23 11:05, Jason Wang wrote:
----- Original Message -----
On 2019/8/22 14:07, Yang Yingliang wrote:
On 2019/8/22 10:13, Jason Wang wrote:
On 2019/8/20 上午10:28, Jason Wang wrote:
On 2019/8/20 上午9:25, David Miller wrote:
From: Yang Yingliang <yangyingli...@huawei.com>
Date: Mon, 19 Aug 2019 21:31:19 +0800
Call tun_attach() after register_netdevice() to make sure
tfile->tun
is not published until the netdevice is registered. So the
read/write
thread can not use the tun pointer that may freed by
free_netdev().
(The tun and dev pointer are allocated by alloc_netdev_mqs(),
they
can
be freed by netdev_freemem().)
register_netdevice() must always be the last operation in the
order of
network device setup.
At the point register_netdevice() is called, the device is visible
globally
and therefore all of it's software state must be fully
initialized and
ready for us.
You're going to have to find another solution to these problems.
The device is loosely coupled with sockets/queues. Each side is
allowed to be go away without caring the other side. So in this
case, there's a small window that network stack think the device
has
one queue but actually not, the code can then safely drop them.
Maybe it's ok here with some comments?
Or if not, we can try to hold the device before tun_attach and drop
it after register_netdevice().
Hi Yang:
I think maybe we can try to hold refcnt instead of playing real num
queues here. Do you want to post a V4?
I think the refcnt can prevent freeing the memory in this case.
When register_netdevice() failed, free_netdev() will be called
directly,
dev->pcpu_refcnt and dev are freed without checking refcnt of dev.
How about using patch-v1 that using a flag to check whether the device
registered successfully.
As I said, it lacks sufficient locks or barriers. To be clear, I meant
something like (compile-test only):
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index db16d7a13e00..e52678f9f049 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2828,6 +2828,7 @@ static int tun_set_iff(struct net *net, struct
file *file, struct ifreq *ifr)
(ifr->ifr_flags & TUN_FEATURES);
INIT_LIST_HEAD(&tun->disabled);
+ dev_hold(dev);
err = tun_attach(tun, file, false, ifr->ifr_flags &
IFF_NAPI,
ifr->ifr_flags & IFF_NAPI_FRAGS);
if (err < 0)
@@ -2836,6 +2837,7 @@ static int tun_set_iff(struct net *net, struct
file *file, struct ifreq *ifr)
err = register_netdevice(tun->dev);
if (err < 0)
goto err_detach;
+ dev_put(dev);
}
netif_carrier_on(tun->dev);
@@ -2852,11 +2854,13 @@ static int tun_set_iff(struct net *net,
struct file *file, struct ifreq *ifr)
return 0;
err_detach:
+ dev_put(dev);
tun_detach_all(dev);
/* register_netdevice() already called tun_free_netdev() */
goto err_free_dev;
err_free_flow:
+ dev_put(dev);
tun_flow_uninit(tun);
security_tun_dev_free_security(tun->security);
err_free_stat:
What's your thought?
The dev pointer are freed without checking the refcount in
free_netdev() called by err_free_dev
path, so I don't understand how the refcount protects this pointer.
The refcount are guaranteed to be zero there, isn't it?
No, it's not.
err_free_dev:
free_netdev(dev);
void free_netdev(struct net_device *dev)
{
...
/* pcpu_refcnt can be freed without checking refcount */
free_percpu(dev->pcpu_refcnt);
dev->pcpu_refcnt = NULL;
/* Compatibility with error handling in drivers */
if (dev->reg_state == NETREG_UNINITIALIZED) {
/* dev can be freed without checking refcount */
netdev_freemem(dev);
return;
}
...
}
Thanks
Thanks,
Yang
Thanks
.
.
