[PATCH v3 2/2] net: postpone net device uevent to fix a race

From: Kalle Valo <redacted>

There's a race in register_netdevice() so that the udev event is sent before
the device is actually ready. This was visible with flimflam, chrome os
connection manager:

00:21:35 roska flimflamd[2598]: src/udev.c:add_net_device()
00:21:35 roska flimflamd[2598]: connman_inet_ifname: SIOCGIFNAME(index
   4): No such device

So the kobject is visible in udev before the device is ready.

The issue is reported here:

https://bugzilla.kernel.org/show_bug.cgi?id=15606

Fix this by postponing the uevent with device_add_noevent() and
calling device_uevent() once the device is really ready.

Thanks to Johannes Berg for the original idea.

Signed-off-by: Kalle Valo <redacted>
---
 net/core/dev.c       |    3 +++
 net/core/net-sysfs.c |    2 +-
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 856b6ee..80cfa23 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -5454,6 +5454,9 @@ int register_netdevice(struct net_device *dev)
 		rollback_registered(dev);
 		dev->reg_state = NETREG_UNREGISTERED;
 	}
+
+	device_uevent(&(dev->dev));
+
 	/*
 	 *	Prevent userspace races by waiting until the network
 	 *	device is fully setup before sending notifications.

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 5ceb257..c10b1d5 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c

@@ -1337,7 +1337,7 @@ int netdev_register_kobject(struct net_device *net)
 #endif
 #endif /* CONFIG_SYSFS */
 
-	error = device_add(dev);
+	error = device_add_noevent(dev);
 	if (error)
 		return error;