Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace()

[Steven Rostedt]

On Thu, 03 Oct 2019 09:39:17 +0100
David Howells <dhowells@xxxxxxxxxx> wrote:

> paulmck@xxxxxxxxxx wrote:
> 
> > +#define rcu_replace(rcu_ptr, ptr, c)					\
> > +({									\
> > +	typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));	\
> > +	rcu_assign_pointer((rcu_ptr), (ptr));				\
> > +	__tmp;								\
> > +})  
> 
> Does it make sense to actually use xchg() if that's supported by the arch?
> 

Hmm, is there really any arch that doesn't support xchg()? It would be
very hard to do any kind of atomic operations without it.

cmpxchg() is the one that I understand is optional by the arch.

-- Steve