linux-kernel - [PATCH] smpboot: correctly update number of booted cores

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Message-Id: <20180221205036.5244-1-sneves@dei.uc.pt>
Date:   Wed, 21 Feb 2018 20:50:36 +0000
From:   Samuel Neves <sneves@....uc.pt>
To:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, jgross@...e.com, douly.fnst@...fujitsu.com,
        luto@...nel.org, prarit@...hat.com, ak@...ux.intel.com,
        vkuznets@...hat.com, linux-kernel@...r.kernel.org
Cc:     Samuel Neves <sneves@....uc.pt>
Subject: [PATCH] smpboot: correctly update number of booted cores

Without this fix, /proc/cpuinfo will display an incorrect amount
of CPU cores, after bringing them offline and online again, as
exemplified below:

$ cat /proc/cpuinfo | grep cores
cpu cores	: 4
cpu cores	: 8
cpu cores	: 8
cpu cores	: 20
cpu cores	: 4
cpu cores	: 3
cpu cores	: 2
cpu cores	: 2

This patch fixes this by always zeroing the booted_cores variable
upon turning off a logical CPU.

Signed-off-by: Samuel Neves <sneves@....uc.pt>
---
 arch/x86/kernel/smpboot.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 9eee25d07586..ff99e2b6fc54 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1437,6 +1437,7 @@ static void remove_siblinginfo(int cpu)
 	cpumask_clear(topology_sibling_cpumask(cpu));
 	cpumask_clear(topology_core_cpumask(cpu));
 	c->cpu_core_id = 0;
+	c->booted_cores = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
 	recompute_smt_state();
 }
-- 
2.14.3