Re: [RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET

["H. Peter Anvin" <hpa@linux.intel.com>]

On 03/29/2011 02:47 PM, Paul E. McKenney wrote:
> On Tue, Mar 29, 2011 at 02:32:30PM -0700, H. Peter Anvin wrote:
>> On 03/29/2011 02:31 PM, Paul E. McKenney wrote:
>>>>
>>>> I have to say that if we have to use hardcoded offsets in C then we have
>>>> bigger problems.
>>>
>>> In this case, the offsets are mechanically generated from the structure
>>> definitions.
>>>
>>> Or am I missing your point?
>>
>> Yes.  The point is if we have to pull out these kinds of hacks in *C*
>> code, we are doing it wrong.  Not just a little wrong, but completely
>> and totally bonkers wrong.
> 
> OK, maybe we are doing it wrong.
> 
> But in that case, how do you suggest restructuring include/linux/sched.h
> so that struct task_struct can be safely included everywhere
> rcu_read_lock() and friends are invoked?  Or, on the other hand,
> what should we be doing so that we don't need to include task_struct
> everywhere?
> 

Lai's text doesn't give any hint as to the specific nature of the
conflict, which makes it hard to come up with a better alternative
without having to rediscover the problem from first principles.
However, a somewhat logical assumption is that the problem is that
struct task_struct includes struct rcu_head, in which case the easiest
thing to do is almost certainly to move the definition of struct
rcu_head to its own header file, <linux/rcuhead.h>, and include that in
<linux/sched.h>, which should make it possible to include
<linux/sched.h> in <linux/rcupdate.h>.

	-hpa