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Subject: Re: [patch V4 33/37] cpu/hotplug: Allow "parallel" bringup up to
 CPUHP_BP_KICK_AP_STATE
In-Reply-To: <2ed3ff77-c973-4e23-9e2f-f10776e432b7@sirena.org.uk>
References: <20230512203426.452963764@linutronix.de>
 <20230512205257.240231377@linutronix.de>
 <4ca39e58-055f-432c-8124-7c747fa4e85b@sirena.org.uk> <87bkicw01a.ffs@tglx>
 <2ed3ff77-c973-4e23-9e2f-f10776e432b7@sirena.org.uk>
Date:   Tue, 23 May 2023 01:12:26 +0200
Message-ID: <87wn10ufj9.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Mon, May 22 2023 at 23:27, Mark Brown wrote:
> On Mon, May 22, 2023 at 11:04:17PM +0200, Thomas Gleixner wrote:
>
>> That does not make any sense at all and my tired brain does not help
>> either.
>
>> Can you please apply the below debug patch and provide the output?
>
> Here's the log, a quick glance says the 
>
> 	if (!--ncpus)
> 		break;
>
> check is doing the wrong thing

Obviously.

Let me find a brown paperbag and go to sleep before I even try to
compile the obvious fix.

---
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 005f863a3d2b..88a7ede322bd 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1770,9 +1770,6 @@ static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int n
 	for_each_cpu(cpu, mask) {
 		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
-		if (!--ncpus)
-			break;
-
 		if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
 			/*
 			 * If this failed then cpu_up() might have only
@@ -1781,6 +1778,9 @@ static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int n
 			 */
 			WARN_ON(cpuhp_invoke_callback_range(false, cpu, st, CPUHP_OFFLINE));
 		}
+
+		if (!--ncpus)
+			break;
 	}
 }