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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: <20230509101902.GV83892@hirez.programming.kicks-ass.net>
References: <20230508181633.089804905@linutronix.de>
 <20230508185217.671595388@linutronix.de>
 <20230509101902.GV83892@hirez.programming.kicks-ass.net>
Date:   Tue, 09 May 2023 20:03:32 +0200
Message-ID: <87lehxz8jv.ffs@tglx>
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On Tue, May 09 2023 at 12:19, Peter Zijlstra wrote:
> Again, not really this patch, but since I had to look at this code ....
>
> On Mon, May 08, 2023 at 09:43:39PM +0200, Thomas Gleixner wrote:
>> @@ -1048,60 +1066,89 @@ static int do_boot_cpu(int apicid, int c
>
> 	/*
> 	 * AP might wait on cpu_callout_mask in cpu_init() with
> 	 * cpu_initialized_mask set if previous attempt to online
> 	 * it timed-out. Clear cpu_initialized_mask so that after
> 	 * INIT/SIPI it could start with a clean state.
> 	 */
> 	cpumask_clear_cpu(cpu, cpu_initialized_mask);
> 	smp_mb();
>
> ^^^ that barrier is weird too, cpumask_clear_cpu() is an atomic op and
> implies much the same (this is x86 after all). If you want to be super
> explicit about it write:
>
> 	smp_mb__after_atomic();
>
> (which is a no-op) but then it still very much requires a comment as to
> what exactly it orders against what.

Won't bother either as that mask is gone a few patches later.