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Date:   Tue, 9 May 2023 13:35:48 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        David Woodhouse <dwmw2@infradead.org>,
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Subject: Re: [patch v3 18/36] [patch V2 18/38] cpu/hotplug: Add CPU state
 tracking and synchronization
Message-ID: <20230509113548.GD38236@hirez.programming.kicks-ass.net>
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 <20230508185218.240871842@linutronix.de>
 <20230509110722.GZ83892@hirez.programming.kicks-ass.net>
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On Tue, May 09, 2023 at 01:07:23PM +0200, Peter Zijlstra wrote:
> On Mon, May 08, 2023 at 09:43:55PM +0200, Thomas Gleixner wrote:
> 
> > +static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
> > +{
> > +	atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
> > +	int sync = atomic_read(st);
> > +
> > +	while (!atomic_try_cmpxchg(st, &sync, state));
> > +}
> 
> Why isn't:
> 
> 	atomic_set(st, state);
> 
> any good?

Hmm, should at the very least be atomic_set_release(), but if you want
the full barrier then:

	(void)atomic_xchg(st, state);

is the much saner way to write the above.