linux-kernel - Re: [patch V4 33/37] cpu/hotplug: Allow "parallel" bringup up to CPUHP_BP_KICK_AP

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Message-ID: <87wn10ufj9.ffs@tglx>
Date:   Tue, 23 May 2023 01:12:26 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        David Woodhouse <dwmw2@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        linux-csky@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Ross Philipson <ross.philipson@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [patch V4 33/37] cpu/hotplug: Allow "parallel" bringup up to
 CPUHP_BP_KICK_AP_STATE

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;
 	}
 }