queue-4.19/cpu-hotplug-mute-hotplug-lockdep-during-init.patch

   1 From 39f7e50ea91f5da025fcdbc731e2b2424088b567 Mon Sep 17 00:00:00 2001
   2 From: Valentin Schneider <valentin.schneider@arm.com>
   3 Date: Wed, 19 Dec 2018 18:23:15 +0000
   4 Subject: cpu/hotplug: Mute hotplug lockdep during init
   5
   6 [ Upstream commit ce48c457b95316b9a01b5aa9d4456ce820df94b4 ]
   7
   8 Since we've had:
   9
  10   commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")
  11
  12 we've been getting some lockdep warnings during init, such as on HiKey960:
  13
  14 [    0.820495] WARNING: CPU: 4 PID: 0 at kernel/cpu.c:316 lockdep_assert_cpus_held+0x3c/0x48
  15 [    0.820498] Modules linked in:
  16 [    0.820509] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G S                4.20.0-rc5-00051-g4cae42a #34
  17 [    0.820511] Hardware name: HiKey960 (DT)
  18 [    0.820516] pstate: 600001c5 (nZCv dAIF -PAN -UAO)
  19 [    0.820520] pc : lockdep_assert_cpus_held+0x3c/0x48
  20 [    0.820523] lr : lockdep_assert_cpus_held+0x38/0x48
  21 [    0.820526] sp : ffff00000a9cbe50
  22 [    0.820528] x29: ffff00000a9cbe50 x28: 0000000000000000
  23 [    0.820533] x27: 00008000b69e5000 x26: ffff8000bff4cfe0
  24 [    0.820537] x25: ffff000008ba69e0 x24: 0000000000000001
  25 [    0.820541] x23: ffff000008fce000 x22: ffff000008ba70c8
  26 [    0.820545] x21: 0000000000000001 x20: 0000000000000003
  27 [    0.820548] x19: ffff00000a35d628 x18: ffffffffffffffff
  28 [    0.820552] x17: 0000000000000000 x16: 0000000000000000
  29 [    0.820556] x15: ffff00000958f848 x14: 455f3052464d4d34
  30 [    0.820559] x13: 00000000769dde98 x12: ffff8000bf3f65a8
  31 [    0.820564] x11: 0000000000000000 x10: ffff00000958f848
  32 [    0.820567] x9 : ffff000009592000 x8 : ffff00000958f848
  33 [    0.820571] x7 : ffff00000818ffa0 x6 : 0000000000000000
  34 [    0.820574] x5 : 0000000000000000 x4 : 0000000000000001
  35 [    0.820578] x3 : 0000000000000000 x2 : 0000000000000001
  36 [    0.820582] x1 : 00000000ffffffff x0 : 0000000000000000
  37 [    0.820587] Call trace:
  38 [    0.820591]  lockdep_assert_cpus_held+0x3c/0x48
  39 [    0.820598]  static_key_enable_cpuslocked+0x28/0xd0
  40 [    0.820606]  arch_timer_check_ool_workaround+0xe8/0x228
  41 [    0.820610]  arch_timer_starting_cpu+0xe4/0x2d8
  42 [    0.820615]  cpuhp_invoke_callback+0xe8/0xd08
  43 [    0.820619]  notify_cpu_starting+0x80/0xb8
  44 [    0.820625]  secondary_start_kernel+0x118/0x1d0
  45
  46 We've also had a similar warning in sched_init_smp() for every
  47 asymmetric system that would enable the sched_asym_cpucapacity static
  48 key, although that was singled out in:
  49
  50   commit 40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()")
  51
  52 Those warnings are actually harmless, since we cannot have hotplug
  53 operations at the time they appear. Instead of starting to sprinkle
  54 useless hotplug lock operations in the init codepaths, mute the
  55 warnings until they start warning about real problems.
  56
  57 Suggested-by: Peter Zijlstra <peterz@infradead.org>
  58 Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
  59 Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
  60 Cc: Andrew Morton <akpm@linux-foundation.org>
  61 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  62 Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  63 Cc: Thomas Gleixner <tglx@linutronix.de>
  64 Cc: Will Deacon <will.deacon@arm.com>
  65 Cc: cai@gmx.us
  66 Cc: daniel.lezcano@linaro.org
  67 Cc: dietmar.eggemann@arm.com
  68 Cc: linux-arm-kernel@lists.infradead.org
  69 Cc: longman@redhat.com
  70 Cc: marc.zyngier@arm.com
  71 Cc: mark.rutland@arm.com
  72 Link: https://lkml.kernel.org/r/1545243796-23224-2-git-send-email-valentin.schneider@arm.com
  73 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  74 Signed-off-by: Sasha Levin <sashal@kernel.org>
  75 ---
  76  kernel/cpu.c | 9 +++++++++
  77  1 file changed, 9 insertions(+)
  78
  79 diff --git a/kernel/cpu.c b/kernel/cpu.c
  80 index 9d0ecc4a0e79..dc250ec2c096 100644
  81 --- a/kernel/cpu.c
  82 +++ b/kernel/cpu.c
  83 @@ -313,6 +313,15 @@ void cpus_write_unlock(void)
  84
  85  void lockdep_assert_cpus_held(void)
  86  {
  87 +       /*
  88 +        * We can't have hotplug operations before userspace starts running,
  89 +        * and some init codepaths will knowingly not take the hotplug lock.
  90 +        * This is all valid, so mute lockdep until it makes sense to report
  91 +        * unheld locks.
  92 +        */
  93 +       if (system_state < SYSTEM_RUNNING)
  94 +               return;
  95 +
  96         percpu_rwsem_assert_held(&cpu_hotplug_lock);
  97  }
  98
  99 --
 100 2.19.1
 101