[RFC] Handling kernel stack overflows

[Eric W. Biederman]

Well we currently keep a struct thread_info on the stack
which while not as bad as task_struct has it's own uses
and implications which may limit what you are trying
to do.

That said a function like:

int call_on_new_stack(int (*continuation)(void *), void *closure)
{
	struct task_struct *tsk;
	struct thread_info *ti;

	if (plenty_of_stack_space())
		return continuation(closure);

	tsk = current();
	ti = alloc_thread_info(tsk);
	if (!ti)
		return -ENOMEM;

	setup_extra_thread_info(tsk, ti, continuation, closure);
	schedule();
}

Might make sense.  Last I heard the block layer and xfs seemed
to have largely solved their problems with running short on stack
space, so I don't know if it is necessary but it certainly sounds
relatively simple and interesting.

Running short on stack space is a recurring theme so a function that
allows us to have a little more when we really need it and be able to
switch even x86_64 to 4K stacks would be interesting.

I'm not quite certain where we could insert calls to call_on_new_stack,
but it looks simple enough that it is worth coding up and playing
with.  If the results are good it could be worth merging.

Eric