Date: Tue, 26 Aug 2008 00:46:07 -0700 (PDT)
Message-Id: <20080826.004607.253712060.davem@davemloft.net>
To: mingo@elte.hu
Cc: torvalds@linux-foundation.org, Alan.Brunelle@hp.com, travis@sgi.com,
       tglx@linutronix.de, rjw@sisk.pl, linux-kernel@vger.kernel.org,
       kernel-testers@vger.kernel.org, akpm@linux-foundation.org,
       arjan@linux.intel.com, rusty@rustcorp.com.au
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -
 bisected
From: David Miller <davem@davemloft.net>
In-Reply-To: <20080826072220.GB31876@elte.hu>
References: <alpine.LFD.1.10.0808251344250.3363@nehalem.linux-foundation.org>
	<alpine.LFD.1.10.0808251401590.3363@nehalem.linux-foundation.org>
	<20080826072220.GB31876@elte.hu>
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From: Ingo Molnar <mingo@elte.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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