Re: Possible race with br_del_if()

* Stephen Hemminger [off-list ref] [2005-08-18 17:36]:

On Thu, 18 Aug 2005 17:23:23 -0500
Ryan Harper [off-list ref] wrote:

quoted

* Stephen Hemminger [off-list ref] [2005-08-18 17:11]:

quoted

On Thu, 18 Aug 2005 16:40:36 -0500
Ryan Harper [off-list ref] wrote:

quoted

Hello,

I've encountered several oops when adding and removing interfaces from
bridges while using Xen.  Most of the details are available [1]here.
The short of it is the following sequence:

Doesn't the mutex in RTNL work right?  or are you calling
routines with out asserting it?

unregister_netdevice asserts RTNL, add_del_if() in br_ioctl.c doesn't
seem to do so.  I don't see it down dev_get_by_index() path either.  It
looks like any caller of add_del_if() isn't asserting RTNL.  The two
callers I see are:

br_dev_ioctl() in br_ioctl.c
old_dev_ioctl() in br_ioctl.c

But the pat to br_dev_ioctl() is via the socket ioctl and that
should already have gotten RTNL.


dev_ioctl
	rtnl_lock()
	dev_ifsioc()
		dev->do_ioctl --> br_dev_ioctl

Hrm. OK.  It sounds like both paths are doing the right thing w.r.t
asserting RTNL, but br_device_event() still gets called with:

1) dev->br_port != NULL 
2) dev->br_port->state = BR_STATE_DISABLED
3) event = NETDEV_UNREGISTER

which results in br_del_if() being called a second time on the same
port.  

Some of the other cases  (NETDEV_FEAT_CHANGE, NETDEV_CHANGE) do a state
check before calling a subsequent function.  Does it make sense for
br_del_if() to be called on a port whose state is BR_STATE_DISABLED?

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com