[PATCH 3.18 071/185] x86/topology: Update the cpu cores field in /proc/cpuinfo correctly across CPU hotplug operations

[Greg Kroah-Hartman]

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

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

From: Samuel Neves <sneves@xxxxxxxxx>

[ 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@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>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/smpboot.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1290,6 +1290,7 @@ static void remove_siblinginfo(int cpu)
 	cpumask_clear(cpu_core_mask(cpu));
 	c->phys_proc_id = 0;
 	c->cpu_core_id = 0;
+	c->booted_cores = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
 }