linux-kernel - [tip:smp/hotplug] cpuhotplug: Link lock stacks for hotplug callbacks

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Date:   Fri, 26 May 2017 01:48:59 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     paulmck@...ux.vnet.ibm.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...nel.org,
        rostedt@...dmis.org, hpa@...or.com, peterz@...radead.org
Subject: [tip:smp/hotplug] cpuhotplug: Link lock stacks for hotplug
 callbacks

Commit-ID:  49dfe2a6779717d9c18395684ee31bdc98b22e53
Gitweb:     http://git.kernel.org/tip/49dfe2a6779717d9c18395684ee31bdc98b22e53
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Wed, 24 May 2017 10:15:43 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 26 May 2017 10:10:48 +0200

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@...utronix.de>
Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sebastian Siewior <bigeasy@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
Link: http://lkml.kernel.org/r/20170524081549.709375845@linutronix.de

---
 kernel/cpu.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6683621..7435ffc 100644
--- 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
@@ -403,6 +409,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 
 	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) {
@@ -429,6 +436,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 		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);
 }
@@ -443,6 +451,9 @@ cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
 	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.
@@ -486,6 +497,8 @@ static int cpuhp_kick_ap_work(unsigned int cpu)
 	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);