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   1 From foo@baz Sun May 27 16:52:54 CEST 2018
   2 From: Samuel Neves <sneves@dei.uc.pt>
   3 Date: Wed, 21 Feb 2018 20:50:36 +0000
   4 Subject: x86/topology: Update the 'cpu cores' field in /proc/cpuinfo correctly across CPU hotplug operations
   5
   6 From: Samuel Neves <sneves@dei.uc.pt>
   7
   8 [ Upstream commit 4596749339e06dc7a424fc08a15eded850ed78b7 ]
   9
  10 Without this fix, /proc/cpuinfo will display an incorrect amount
  11 of CPU cores, after bringing them offline and online again, as
  12 exemplified below:
  13
  14   $ cat /proc/cpuinfo | grep cores
  15   cpu cores     : 4
  16   cpu cores     : 8
  17   cpu cores     : 8
  18   cpu cores     : 20
  19   cpu cores     : 4
  20   cpu cores     : 3
  21   cpu cores     : 2
  22   cpu cores     : 2
  23
  24 This patch fixes this by always zeroing the booted_cores variable
  25 upon turning off a logical CPU.
  26
  27 Tested-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
  28 Signed-off-by: Samuel Neves <sneves@dei.uc.pt>
  29 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  30 Cc: Peter Zijlstra <peterz@infradead.org>
  31 Cc: Thomas Gleixner <tglx@linutronix.de>
  32 Cc: jgross@suse.com
  33 Cc: luto@kernel.org
  34 Cc: prarit@redhat.com
  35 Cc: vkuznets@redhat.com
  36 Link: http://lkml.kernel.org/r/20180221205036.5244-1-sneves@dei.uc.pt
  37 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  38 Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
  39 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  40 ---
  41  arch/x86/kernel/smpboot.c |    1 +
  42  1 file changed, 1 insertion(+)
  43
  44 --- a/arch/x86/kernel/smpboot.c
  45 +++ b/arch/x86/kernel/smpboot.c
  46 @@ -1521,6 +1521,7 @@ static void remove_siblinginfo(int cpu)
  47         cpumask_clear(topology_core_cpumask(cpu));
  48         c->phys_proc_id = 0;
  49         c->cpu_core_id = 0;
  50 +       c->booted_cores = 0;
  51         cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
  52         recompute_smt_state();
  53  }