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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Mar 29, 2011 at 03:01:19PM -0700, H. Peter Anvin wrote:
> 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>.

I believe that there are other circular dependencies -- there certainly
were a few years back -- but I will defer to Lai.

							Thanx, Paul