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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [patch v3 08/36] x86/smpboot: Split up native_cpu_up() into
 separate phases and document them
In-Reply-To: <20230509100421.GU83892@hirez.programming.kicks-ass.net>
References: <20230508181633.089804905@linutronix.de>
 <20230508185217.671595388@linutronix.de>
 <20230509100421.GU83892@hirez.programming.kicks-ass.net>
Date:   Tue, 09 May 2023 22:11:05 +0200
Message-ID: <87fs85z2na.ffs@tglx>
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On Tue, May 09 2023 at 12:04, Peter Zijlstra wrote:
> On Mon, May 08, 2023 at 09:43:39PM +0200, Thomas Gleixner wrote:
> Not to the detriment of this patch, but this barrier() and it's comment
> seem weird vs smp_callin(). That function ends with an atomic bitop (it
> has to, at the very least it must not be weaker than store-release) but
> also has an explicit wmb() to order setup vs CPU_STARTING.
>
> (arguably that should be a full fence *AND* get a comment)

TBH: I'm grasping for something 'arguable': What's the point of this
wmb() or even a mb()?

Most of the [w]mb()'s in smpboot.c except those in mwait_play_dead()
have a very distinct voodoo programming smell.

Thanks,

        tglx