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Subject: [PATCH] perf/x86/intel/rapl: Rename rapl_cpu_prepare() to
 rapl_cpu_starting()
To: linux-kernel@vger.kernel.org, x86@kernel.org
From: Yasuaki Ishimatsu <yasu.isimatu@gmail.com>
Cc: tglx@linutronix.de
Message-ID: <9063c543-880e-0b12-0671-1492182990e7@gmail.com>
Date: Tue, 24 Jan 2017 12:03:33 -0500
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rapl_cpu_prepare() must be called after logical package id of CPU
is set by topology_update_package_map().

But when onlining hot-added CPU, rapl_cpu_prepare() is called before
setting logical package id of the hot-added CPU. So cpu_to_rapl_pmu()
in rapl_cpu_prepare() finds a rapl_pmu of wrong logical package id and
rapl_cpu_prepare() initializes the wrong rapl_pmu.

After that logical package id of the hot-added CPU is set by
topology_update_package_map(). But rapl_cpu_prepare() does
not initialize pmu of the logical package id of the hot-added CPU.
So when calling rapl_cpu_online(), cpu_to_rapl_pmu() returns NULL and
the following NULL pointer dereference occurs.

   BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
   IP: rapl_cpu_online+0x8d/0xb0
   <snip>
   Call Trace:
    ? rapl_cpu_offline+0xc0/0xc0
    cpuhp_invoke_callback+0x8d/0x3f0
    cpuhp_up_callbacks+0x37/0xb0
    cpuhp_thread_fun+0xc9/0xe0
    smpboot_thread_fn+0x110/0x160
    kthread+0x101/0x140
    ? sort_range+0x30/0x30
    ? kthread_park+0x90/0x90
    ret_from_fork+0x25/0x30

The patch renames rapl_cpu_prepare() to rapl_cpu_starting() and changes
the position of cpuhp_state so that rapl_cpu_starting() is called
after topology_update_package_map().

Fixes: 9de8d686955b ("perf/x86/intel/rapl: Convert it to a per package facility")
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
CC: Thomas Gleixner <tglx@linutronix.de>
---
  arch/x86/events/intel/rapl.c | 11 ++++++-----
  include/linux/cpuhotplug.h   |  2 +-
  2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/events/intel/rapl.c b/arch/x86/events/intel/rapl.c
index 17c3564..f762cd6 100644
--- a/arch/x86/events/intel/rapl.c
+++ b/arch/x86/events/intel/rapl.c
@@ -598,7 +598,7 @@ static int rapl_cpu_online(unsigned int cpu)
  	return 0;
  }

-static int rapl_cpu_prepare(unsigned int cpu)
+static int rapl_cpu_starting(unsigned int cpu)
  {
  	struct rapl_pmu *pmu = cpu_to_rapl_pmu(cpu);

@@ -804,8 +804,9 @@ static int __init rapl_pmu_init(void)
  	 * Install callbacks. Core will call them for each online cpu.
  	 */

-	ret = cpuhp_setup_state(CPUHP_PERF_X86_RAPL_PREP, "perf/x86/rapl:prepare",
-				rapl_cpu_prepare, NULL);
+	ret = cpuhp_setup_state(CPUHP_AP_PERF_X86_RAPL_STARTING,
+				"perf/x86/rapl:starting",
+				rapl_cpu_starting, NULL);
  	if (ret)
  		goto out;

@@ -825,7 +826,7 @@ static int __init rapl_pmu_init(void)
  out2:
  	cpuhp_remove_state(CPUHP_AP_PERF_X86_RAPL_ONLINE);
  out1:
-	cpuhp_remove_state(CPUHP_PERF_X86_RAPL_PREP);
+	cpuhp_remove_state(CPUHP_AP_PERF_X86_RAPL_STARTING);
  out:
  	pr_warn("Initialization failed (%d), disabled\n", ret);
  	cleanup_rapl_pmus();
@@ -836,7 +837,7 @@ static int __init rapl_pmu_init(void)
  static void __exit intel_rapl_exit(void)
  {
  	cpuhp_remove_state_nocalls(CPUHP_AP_PERF_X86_RAPL_ONLINE);
-	cpuhp_remove_state_nocalls(CPUHP_PERF_X86_RAPL_PREP);
+	cpuhp_remove_state_nocalls(CPUHP_AP_PERF_X86_RAPL_STARTING);
  	perf_pmu_unregister(&rapl_pmus->pmu);
  	cleanup_rapl_pmus();
  }
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index d936a00..63da322 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -10,7 +10,6 @@ enum cpuhp_state {
  	CPUHP_PERF_X86_PREPARE,
  	CPUHP_PERF_X86_UNCORE_PREP,
  	CPUHP_PERF_X86_AMD_UNCORE_PREP,
-	CPUHP_PERF_X86_RAPL_PREP,
  	CPUHP_PERF_BFIN,
  	CPUHP_PERF_POWER,
  	CPUHP_PERF_SUPERH,
@@ -90,6 +89,7 @@ enum cpuhp_state {
  	CPUHP_AP_PERF_X86_AMD_UNCORE_STARTING,
  	CPUHP_AP_PERF_X86_STARTING,
  	CPUHP_AP_PERF_X86_AMD_IBS_STARTING,
+	CPUHP_AP_PERF_X86_RAPL_STARTING,
  	CPUHP_AP_PERF_X86_CQM_STARTING,
  	CPUHP_AP_PERF_X86_CSTATE_STARTING,
  	CPUHP_AP_PERF_XTENSA_STARTING,
-- 
1.8.3.1