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Date:   Thu, 3 Oct 2019 09:08:50 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     David Howells <dhowells@redhat.com>
Cc:     paulmck@kernel.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org, mingo@kernel.org,
        jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
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        Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Shane M Seymour <shane.seymour@hpe.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>
Subject: Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to
 rcu_replace()
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On Thu, 03 Oct 2019 09:39:17 +0100
David Howells <dhowells@redhat.com> wrote:

> paulmck@kernel.org 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