Problem with notifier_lock in notifier_chain_unregister with 2.4.

[Adam Radford]

I am trying create a patch for the 3ware driver to have it notify the cards
firmware
of a pending shutdown using register_reboot_notifier() and
unregister_reboot_notifier().

The problem is that under SMP, the system gets partially hung in
notifier_chain_unregister()
in kernel/sys.c in this area:

int notifier_chain_unregister(struct notifier_block **nl, struct
notifier_block *n)
{
	write_lock (&notifier_lock);         ---->  The system gets stuck
right here and never gets this lock
	while ((*nl)!=NULL) 
	{ 
		if ((*nl)==n)
		{
			*nl=n->next;
			write_unlock(&notifier_lock);
			return 0;
		}
		nl=&(*nl)->next);
	}
	write_unlock(&notifier_lock);
	return -ENOENT;
}

It is probably worth noting that the 2.2.X kernels don't have this lock
scheme, and removing it fixes the
problem.   Is this lock scheme correct in 2.4.0 ?

--
Adam Radford
Software Engineer
3ware, Inc.