Re: Adding PCMCIA support to the kernel tree -- developers needed.

["Andrew Morton" <morton@nortelnetworks.com>]

David Brownell wrote:
> 
> My short version of "why did that change" was that the addition of
> network hotplugging turned up some races (the network driver API
> wasn't designed for hotplugging, unlike USB or PCI, and some locks
> were held so usermode "ifconfig" could deadlock) and changing all
> that was the expedient way out.  Andrew Morton can elaborate;
> from test5 through test11, hotplugging was synchronous, without
> any reported problems when used with USB.

It was a deadlock, not a race.  We were calling `/sbin/hotplug net'
from within register_netdevice, with rtnl_lock held.  /sbin/hotplug
then called `ifconfig up', which wanted to claim rtnl_lock.

My third (and as yet unapplied) call_usermodehelper patch rearranges
the calls to '/sbin/hotplug net' so they happen outside the rtnl_lock,
so I think we could use synchronous-exec mode there.  (We don't have
synchronous exec mode at present - that was the other part of the
patch).

Look.  If we really think we need call_usermodehelper to be synchronous
then let's make a swift and solid decision, present a good case to the boss.

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