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

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Message-ID: <48B4542A.1050004@sgi.com>
Date:	Tue, 26 Aug 2008 12:06:18 -0700
From:	Mike Travis <travis@....com>
To:	David Miller <davem@...emloft.net>
CC:	mingo@...e.hu, torvalds@...ux-foundation.org, Alan.Brunelle@...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

David Miller wrote:
> 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 recently 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.

Yes, I had proposed either modifying, or supplementing a new
smp_call function to pass the cpumask_t as a pointer (similar
to set_cpus_allowed_ptr.)  But an ABI change such as this was
not well received at the time.

Thanks,
Mike
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