On Thu, Feb 14, 2008 at 09:24:27AM -0800, Randy Dunlap wrote:
> On Wed, 13 Feb 2008 14:05:15 -0800 Paul E. McKenney wrote:
>
> > Hello again!
> >
> > This is a speculative patch that as far as I can tell is not yet required.
> > If anyone applies RCU to a data structure allocated out of an array, using
> > array indexes in place of pointers to link the array elements together,
> > then the rcu_assign_index() function in this patch will be needed to
> > assign a given element's array index to the RCU-traversed index. The
> > implementation is exactly that of the old rcu_assign_pointer(), so is
> > extremely well tested.
> >
> > The existing rcu_assign_pointer() will emit a compiler warning in cases
> > where rcu_assign_index() is required.
> >
> > Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
> > ---
> >
> > rcupdate.h | 18 ++++++++++++++++++
> > 1 file changed, 18 insertions(+)
> >
> > diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h
> > linux-2.6.24-rai/include/linux/rcupdate.h
> > --- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13
> > 13:36:47.000000000 -0800
> > +++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13
> > 10:55:40.000000000 -0800
> > @@ -286,6 +286,24 @@ extern struct lockdep_map rcu_lock_map;
> > })
> >
> > /**
> > + * rcu_assign_index - assign (publicize) a index of a newly
> > + * initialized array elementg that will be dereferenced by RCU
> > + * read-side critical sections. Returns the value assigned.
> > + *
> > + * Inserts memory barriers on architectures that require them
> > + * (pretty much all of them other than x86), and also prevents
> > + * the compiler from reordering the code that initializes the
> > + * structure after the index assignment. More importantly, this
> > + * call documents which indexes will be dereferenced by RCU read-side
> > + * code.
> > + */
>
> s/a index/index/
>
> Along with Gautham's typo fix, you could also make this be passable
> kernel-doc notation. :)
Guess I should do the same for rcu_assign_pointer() and probably several
others as well... Good catch!!!
Thanx, Paul
> See Documentation/kernel-doc-nano-HOWTO.txt for details.
>
> Summary:
> The function (or macro) name and short description must be on one line.
> This is followed by the parameters, then a "blank" (actually " *") line,
> then any (longer) description, notes, etc. So basically:
>
> /**
> * rcu_assign_index - assign (publicize) index of a newly initialized array
> element
> * @p: description of @p
> * @v: description of @v
> *
> * This function assigns (publicizes) the index of a newly
> * initialized array element that will be dereferenced by RCU
> * read-side critical sections. Returns the value assigned.
> *
> * Inserts memory barriers on architectures that require them
> * (pretty much all of them other than x86), and also prevents
> * the compiler from reordering the code that initializes the
> * structure after the index assignment. More importantly, this
> * call documents which indexes will be dereferenced by RCU read-side
> * code.
> */
>
>
> > +
> > +#define rcu_assign_index(p, v) ({ \
> > + smp_wmb(); \
> > + (p) = (v); \
> > + })
> > +
> > +/**
> > * synchronize_sched - block until all CPUs have exited any non-preemptive
> > * kernel code sequences.
> > *
>
> ---
> ~Randy
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