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Commit 49dfe2a6 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarIngo 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
parent 0266d81e

kernel/cpu.c

+13 −0
Original line number Diff line number Diff line
@@ -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);