[tip:x86/urgent] x86/topology: Update the 'cpu cores' field in /proc/cpuinfo correctly across CPU hotplug operations

[tip-bot for Samuel Neves]

Commit-ID:  4596749339e06dc7a424fc08a15eded850ed78b7
Gitweb:     https://git.kernel.org/tip/4596749339e06dc7a424fc08a15eded850ed78b7
Author:     Samuel Neves <sneves@xxxxxxxxx>
AuthorDate: Wed, 21 Feb 2018 20:50:36 +0000
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 23 Feb 2018 08:47:47 +0100

x86/topology: Update the 'cpu cores' field in /proc/cpuinfo correctly across CPU hotplug operations

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@xxxxxxxxxxxxxx>
Signed-off-by: Samuel Neves <sneves@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: jgross@xxxxxxxx
Cc: luto@xxxxxxxxxx
Cc: prarit@xxxxxxxxxx
Cc: vkuznets@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20180221205036.5244-1-sneves@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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();
 }