Re: [Bugme-new] [Bug 7952] New: slattach only works every other time

On Mon, 12 Feb 2007 09:36:09 +0100
Jarek Poplawski [off-list ref] wrote:

On 06-02-2007 22:57, Andrew Morton wrote:
...

quoted

First time slattach is run to set up a SLIP line all is ok.
If slattach process is then killed and restarted it fails with message:
SLIP_set_disc(1): File exists
Problem still occurs in 2.6.20rc6 kernel

dmesg shows:
object_add failed for sl0 with -EEXIST, don't try to register things 
with the same name in the same directory.
 [<c01b7b54>] kobject_add+0x147/0x16d
 [<c0211209>] class_device_add+0x9d/0x3b3
 [<c022829d>] register_netdevice+0x21a/0x2d0
 [<c8903213>] slip_open+0x3a1/0x4e2 [slip]
 [<c01fc709>] tty_ioctl+0x922/0xbac

... 

quoted

Steps to reproduce:
(requires a serial port but nothing needs to be attached to it):
# slattach -L -vd -p slip -s 115200 /dev/ttyS0

...

quoted

slip started on /dev/ttyS0 interface sl0

Above is OK, now kill process with CTRL-C

slattach: tty_set_speed: 0
# slattach -L -vd -p slip -s 115200 /dev/ttyS0

...

quoted

SLIP_set_disc(1): File exists

...

quoted

I believe this is called by this changeset :
http://www2.kernel.org/git/?p=linux/kernel/git/stable/linux-2.6.17.y.git;a=commit;h=b17a7c179dd3ce7d04373fddf660eda21efc9db9

I think Martin is probably right here.

It would be useful to check if time has anything to do
with this and wait longer (e.g. >= 1 min.) before the
second slattach.

Anyway, even if there is some other reason, the above
trace shows (IMHO) some inconsistency in register/
unregister_netdevice: if class_device_add is reached
it means the name is valid (so was unregistered) and
EEXIST from netdev_register_sysfs is wrong about the
state of this device. So maybe there should be some
warning plus some delayed action instead of register
cancelled?

Regards,
Jarek P. 

The problem is that the code in sl_alloc() tries to clear out
an net device by calling unregister_netdevice(), the device won't
actually disappear until after rtnl_unlock. This whole idea of
searching for unused devices is racy crap and needs to go.