patches/0032-cpuhotplug-Link-lock-stacks-for-hotplug-callbacks.patch

From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 24 May 2017 10:15:43 +0200
Subject: [PATCH 32/32] cpuhotplug: Link lock stacks for hotplug callbacks

The CPU hotplug callbacks are not covered by lockdep versus the cpu hotplug
rwsem.

CPU0						CPU1
cpuhp_setup_state(STATE, startup, teardown);
 cpus_read_lock();
  invoke_callback_on_ap();
    kick_hotplug_thread(ap);
    wait_for_completion();			hotplug_thread_fn()
    						  lock(m);
						  do_stuff();
						  unlock(m);

Lockdep does not know about this dependency and will not trigger on the
following code sequence:

	  lock(m);
	  cpus_read_lock();

Add a lockdep map and connect the initiators lock chain with the hotplug
thread lock chain, so potential deadlocks can be detected.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170524081549.709375845@linutronix.de
---
 kernel/cpu.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -66,6 +66,12 @@ struct cpuhp_cpu_state {
 
 static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
 
+#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
+static struct lock_class_key cpuhp_state_key;
+static struct lockdep_map cpuhp_state_lock_map =
+	STATIC_LOCKDEP_MAP_INIT("cpuhp_state", &cpuhp_state_key);
+#endif
+
 /**
  * cpuhp_step - Hotplug state machine step
  * @name:	Name of the step
@@ -415,6 +421,7 @@ static void cpuhp_thread_fun(unsigned in
 
 	st->should_run = false;
 
+	lock_map_acquire(&cpuhp_state_lock_map);
 	/* Single callback invocation for [un]install ? */
 	if (st->single) {
 		if (st->cb_state < CPUHP_AP_ONLINE) {
@@ -441,6 +448,7 @@ static void cpuhp_thread_fun(unsigned in
 		else if (st->state > st->target)
 			ret = cpuhp_ap_offline(cpu, st);
 	}
+	lock_map_release(&cpuhp_state_lock_map);
 	st->result = ret;
 	complete(&st->done);
 }
@@ -455,6 +463,9 @@ cpuhp_invoke_ap_callback(int cpu, enum c
 	if (!cpu_online(cpu))
 		return 0;
 
+	lock_map_acquire(&cpuhp_state_lock_map);
+	lock_map_release(&cpuhp_state_lock_map);
+
 	/*
 	 * If we are up and running, use the hotplug thread. For early calls
 	 * we invoke the thread function directly.
@@ -498,6 +509,8 @@ static int cpuhp_kick_ap_work(unsigned i
 	enum cpuhp_state state = st->state;
 
 	trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
+	lock_map_acquire(&cpuhp_state_lock_map);
+	lock_map_release(&cpuhp_state_lock_map);
 	__cpuhp_kick_ap_work(st);
 	wait_for_completion(&st->done);
 	trace_cpuhp_exit(cpu, st->state, state, st->result);