[RFC PATCH 14/49] perf/x86: Move CPUHP_AP_PERF_X86_STARTING post stop_machine()

[Frederic Weisbecker <frederic@kernel.org>]

Between CPUHP_TEARDOWN_CPU and CPUHP_AP_OFFLINE, stop_machine executes
all the teardown callbacks while stopping all CPUs in the system. This
doesn't mix-up well with running RT or isolated tasks.

In order to transition smoothly from global stop_machine to finer
grained synchronization between teardown callbacks and the other CPUs,
a new stop machine post function has been introduced to be executed
after the main one with IRQs still disabled while other CPUs can exit
stop_machine().

Here only intel has a dying callback (intel_pmu_cpu_dying()) which does:

* Deallocate the per CPU DS structure on the MSR_IA32_DS_AREA. This is
  already racy against offlining CPUs because all possible CPUs's MSR
  are written on a hardware event initialization, which still can happen
  before the CPU actually goes off.

* Deallocate PEBS buffer. This is already well synchronized against
  hotplug up callback.

Therefore the related teardwown callback can run concurrently with other
CPUs.

Move it to post stop_machine() accordingly.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 5ac2a925f7d6..c37fa1272d57 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1275,7 +1275,7 @@ void clear_tasks_mm_cpumask(int cpu)
 static int take_cpu_down(void *_param)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
-	enum cpuhp_state target = max((int)st->target, CPUHP_AP_PERF_X86_AMD_UNCORE_STARTING);
+	enum cpuhp_state target = max((int)st->target, CPUHP_AP_PERF_X86_STARTING);
 	int err, cpu = smp_processor_id();
 
 	/* Ensure this CPU doesn't handle any more interrupts. */
@@ -1303,7 +1303,7 @@ static int take_cpu_down_post(void *_param)
 	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
 	int cpu = smp_processor_id();
 
-	WARN_ON(st->state != CPUHP_AP_PERF_X86_AMD_UNCORE_STARTING);
+	WARN_ON(st->state != CPUHP_AP_PERF_X86_STARTING);
 	/*
 	 * Invoke the former CPU_DYING callbacks. DYING must not fail!
 	 */
-- 
2.53.0