linux-kernel - Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c

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Date:	Tue, 26 Aug 2008 00:46:07 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mingo@...e.hu
Cc:	torvalds@...ux-foundation.org, Alan.Brunelle@...com,
	travis@....com, tglx@...utronix.de, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	akpm@...ux-foundation.org, arjan@...ux.intel.com,
	rusty@...tcorp.com.au
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -
 bisected

From: Ingo Molnar <mingo@...e.hu>
Date: Tue, 26 Aug 2008 09:22:20 +0200

> And i guess the next generation of 4K CPUs support should just get away 
> from cpumask_t-on-kernel-stack model altogether, as the current model is 
> not maintainable. We tried the on-kernel-stack variant, and it really 
> does not work reliably. We can fix this in v2.6.28.

I recenetly did some work on sparc64 to use cpumask pointers
as much as possible.

The only case that didn't work was due to a limitation in
arch interfaces for the new generic smp_call_function() code.
It passes a cpumask_t instead of a pointer to one via
arch_send_call_function_ipi().

But other than that, the whole sparc64 SMP stuff uses cpumask_t
pointers only.

What it comes down to is that you have to do the "self cpu"
and other tests in the cross-call dispatch routines themselves,
instead of at the top-level working on cpumask_t objects.

Otherwise you have to modify cpumask_t objects and thus pluck
them onto the stack where they take up silly amounts of space.
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