linux-kernel - [PATCH 4.9 137/329] x86/topology: Update the cpu cores field in /proc/cpuinfo correctly across CPU hotplug operations

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Message-Id: <20180528100254.024411431@linuxfoundation.org>
Date:   Mon, 28 May 2018 12:01:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dou Liyang <douly.fnst@...fujitsu.com>,
        Samuel Neves <sneves@....uc.pt>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, jgross@...e.com,
        luto@...nel.org, prarit@...hat.com, vkuznets@...hat.com,
        Ingo Molnar <mingo@...nel.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.9 137/329] x86/topology: Update the cpu cores field in /proc/cpuinfo correctly across CPU hotplug operations

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Samuel Neves <sneves@....uc.pt>

[ Upstream commit 4596749339e06dc7a424fc08a15eded850ed78b7 ]

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.

Tested-by: Dou Liyang <douly.fnst@...fujitsu.com>
Signed-off-by: Samuel Neves <sneves@....uc.pt>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: jgross@...e.com
Cc: luto@...nel.org
Cc: prarit@...hat.com
Cc: vkuznets@...hat.com
Link: http://lkml.kernel.org/r/20180221205036.5244-1-sneves@dei.uc.pt
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/smpboot.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1497,6 +1497,7 @@ static void remove_siblinginfo(int cpu)
 	cpumask_clear(topology_core_cpumask(cpu));
 	c->phys_proc_id = 0;
 	c->cpu_core_id = 0;
+	c->booted_cores = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
 	recompute_smt_state();
 }