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. :)
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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