linux-kernel - Re: [RFC PATCH 4/5] RCU: Add TASK_RCU

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Message-ID: <4DB12C1E.8050200@cn.fujitsu.com>
Date:	Fri, 22 Apr 2011 15:19:58 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michal Marek <mmarek@...e.cz>,
	Jan Beulich <JBeulich@...ell.com>, Ingo Molnar <mingo@...e.hu>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET

On 04/12/2011 05:02 AM, Paul E. McKenney wrote:
> On Mon, Apr 11, 2011 at 04:31:10PM +0800, Lai Jiangshan wrote:
>> On 04/11/2011 01:12 PM, Paul E. McKenney wrote:
>>
>>> -static inline struct task_struct *next_thread(const struct task_struct *p)
>>> -{
>>> -	return list_entry_rcu(p->thread_group.next,
>>> -			      struct task_struct, thread_group);
>>> -}
>>> +/* Avoid #include hell for inlining rcu_read_lock(). */
>>> +#define next_thread(p) \
>>> +	list_entry_rcu((p)->thread_group.next, struct task_struct, thread_group)
>>>  
>>
>>
>> It is strange for me.
>> The user of the API "next_thread(p)" must has two headers included, sched.h and rculist.h
>>
>> I know this is a very popular pattern of user space code, is it OK for kernel?
>> I think a file(even a header file) uses API(Marco), it should includes the the corresponding
>> headers, it reduces surprises(example, the name of "next_thread()" has no "rcu",
>> it is not expected that rcuxxxx.h is required).
>>
>> I admit the work will become very much simpler if this pattern is allowed.
> 
> The guy who maintains much of sched.h suggested it.  ;-)
> 
> 							Thanx, Paul
> 
>> man fcntl:
>>        #include <unistd.h>
>>        #include <fcntl.h>
>>
>>        int fcntl(int fd, int cmd, ... /* arg */ );
>> --
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> 

Hi, Paul

What is the solution you prefer to?

I insist on the solution which split rcupdate.h into 2 parts,
the first part is rcupdate_defs.h which only contains:
1) struct rcu_head
2) MACRO rcu_dereference*
3) MACRO rcu_access_pointer rcu_access_index rcu_assign_pointer RCU_INIT_POINTER
4) rcu_*_lock_held() which is required by 2)

All of these is required by sched.h, it is all about 450 lines of code.

It does not just separate struct rcu_head out only, because rcu_dereference*()
and APIs in rculist.h are required by in sched.h or headers included by sched.h.

Any suggestion?

Thanks,
Lai
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