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

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Date:	Tue, 30 Sep 2008 09:14:36 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	David Miller <davem@...emloft.net>, Alan.Brunelle@...com,
	tglx@...utronix.de, rjw@...k.pl,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel-testers@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	arjan@...ux.intel.com, Jack Steiner <steiner@....com>
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -	bisected

Ingo Molnar wrote:
> * Mike Travis <travis@....com> wrote:
> 
>>> could you please send whatever .c changes you have already, so that 
>>> we can have a look at how the end result will look like? Doesnt have 
>>> to build, i'm just curious about how it looks like in practice, 
>>> semantically.
>>
>> I will, and the full "allyesconfig" does compile.  And it's basically 
>> a benign change in that the functionality is still the same.  I'm 
>> currently reordering it a bit to clean it up.
> 
> btw., are the resulting instructions also expected to be the same? If 
> yes then you might want to verify it all by making sure the md5's of the 
> .o's do not change.
> 
> (If that's not possible (gcc decides to compile it a bit differently) 
> then no big deal, just wanted to mention the possibility.)
> 
> 	Ingo

Well, not exactly... ;-)  It does institute the new API change that specifies
only pointers to cpumask's can be passed to functions and returned from
functions.  I really wanted the default cpumask_t to be a constant so those
instances where the passed in cpumask is used as a read/write temp variable
would be caught.  But it started getting messy.

One pain is:

	typedef struct __cpumask_s *cpumask_t;
	const cpumask_t xxx;

is not the same as:

	typedef const struct __cpumask_s *const_cpumask_t;
	const_cpumask_t xxx;

and I'm not exactly sure why.  It came up when I tried to declare
functions that returned a constant cpumask_t pointer (node_to_cpumask,
cpumask_of_cpu, etc.)

The other major change I'm contemplating is to remove "cpumask_t" completely
(maybe cpumask_ptr_t?).  This would force every instance of cpumask_t to be
examined.  (I found quite a few I had missed in my original edits when I
added the task struct temp cpumask's.)

Oh yeah, one question ... is "current" always valid?

Thanks,
Mike

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