[PATCH] arm64/smp: Move rcu_cpu_starting() earlier

[Qian Cai]

The call to rcu_cpu_starting() in secondary_start_kernel() is not early
enough in the CPU-hotplug onlining process, which results in lockdep
splats as follows:

 WARNING: suspicious RCU usage
 -----------------------------
 kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 RCU used illegally from offline CPU!
 rcu_scheduler_active = 1, debug_locks = 1
 no locks held by swapper/1/0.

 Call trace:
  dump_backtrace+0x0/0x3c8
  show_stack+0x14/0x60
  dump_stack+0x14c/0x1c4
  lockdep_rcu_suspicious+0x134/0x14c
  __lock_acquire+0x1c30/0x2600
  lock_acquire+0x274/0xc48
  _raw_spin_lock+0xc8/0x140
  vprintk_emit+0x90/0x3d0
  vprintk_default+0x34/0x40
  vprintk_func+0x378/0x590
  printk+0xa8/0xd4
  __cpuinfo_store_cpu+0x71c/0x868
  cpuinfo_store_cpu+0x2c/0xc8
  secondary_start_kernel+0x244/0x318

This is avoided by moving the call to rcu_cpu_starting up near the
beginning of the secondary_start_kernel() function.

Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
Signed-off-by: Qian Cai <cai@xxxxxxxxxx>
---
 arch/arm64/kernel/smp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 82e75fc2c903..09c96f57818c 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -222,6 +222,7 @@ asmlinkage notrace void secondary_start_kernel(void)
 	if (system_uses_irq_prio_masking())
 		init_gic_priority_masking();
 
+	rcu_cpu_starting(cpu);
 	preempt_disable();
 	trace_hardirqs_off();
 
-- 
2.28.0