linux-kernel - Re: [patch 2/3] RCU move trace defines to rcupdate

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Message-ID: <49E81A63.7010700@goop.org>
Date:	Thu, 16 Apr 2009 22:57:55 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [patch 2/3] RCU move trace defines to rcupdate_types.h

Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:
>   
>> On Thu, 16 Apr 2009, Jeremy Fitzhardinge wrote:
>>
>>     
>>> I don't think this helps.  rcupdate_types.h uses preempt_disable/enable, but
>>> doesn't include linux/preempt.h for them - but someone's going to have to, so
>>> you've got an implicit dependency on the user to #include the right headers in
>>> advance.
>>>       
>> Would including linux/preempt.h in rcupdate_types.h be a problem?
>>
>> -- Steve
>>
>>     
>
> I did not include preempt.h in rcupdate_types.h because rcupdate.h did
> not include it, so I thought it had a special status such a kernel.h.
> However, I notice the rcupdate.h includes spinlock.h, which in turn
> includes preempt.h, so we would need to include preempt.h in
> rcupdate_types.h.
>
> But I think preempt.h is pretty much only type definitions. I don't
> think that would be a problem, but maybe Jeremy knows better.

No, preempt.h has fairly complex #include requirements:
#include <linux/thread_info.h>
#include <linux/linkage.h>
#include <linux/list.h>

which in turn include:
/* linux/thread_info */
#include <linux/bitops.h>
#include <asm/thread_info.h>

/* list.h */
#include <linux/stddef.h>
#include <linux/poison.h>
#include <linux/prefetch.h>
#include <asm/system.h>

And from there more complex still:
#include <asm/asm.h>
#include <asm/segment.h>
#include <asm/cpufeature.h>
#include <asm/cmpxchg.h>
#include <asm/nops.h>
#include <linux/kernel.h>
#include <linux/irqflags.h>
#include <asm/page.h>
#include <asm/processor.h>
#include <asm/ftrace.h>
#include <asm/atomic.h>
[...and much more...]

Given that paravirt.h is included in some of those headers, it 
eventually gets cyclic.

    J
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