Re: [PATCH 1/3][RFC] atomic_cmpxchg, atomic_inc_not_zero

[Dipankar Sarma <dipankar@in.ibm.com>]

On Tue, Sep 13, 2005 at 12:51:01AM +1000, Nick Piggin wrote:
> The recent file_table RCU work introduced a new rcuref.h thing,
> which is just begging to be atomic.h. Basically it uses atomic_t,
> digs into the atomic_t type, and also defines its own table of
> spinlocks if the arch doesn't have cmpxchg() thus rendering it
> unsafe for any other atomic_xxx operation to be performed on it.

The rcuref_xxx primitives were for only RCU protected refcounters
and I implemented all the primitives needed for them and use
of them was mandatory.

> Anyway, as it turns out, my lockless pagecache patches have the
> exact same requirement, and so I am proposing to implement two
> new atomic_ primitives that should be useful.
> 
> Only one is actually needed, atomic_inc_not_zero being the exact
> fit for both, however I did atomic_cmpxchg first and it can stay
> around because hopefully will be a generally useful primitive.
> 
> Now atomic_inc_not_zero is not really anything to do with RCU other
> than an RCU protected refcounted structure being an obvious user to
> take a reference on the read side where there is nothing to pin it.
> 
> 1/3 is atomic_cmpxchg, not guaranteed to even compile on most.

This is sooo much better. I would much rather kill rcuref.h
and directly use atomic_inc_not_zero() when necessary.
Please feel free to churn out the whole implementation and I will
test it.

Thanks
Dipankar