Commit 1db49484 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
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smp/hotplug: Hotplug state fail injection 



Add a sysfs file to one-time fail a specific state. This can be used
to test the state rollback code paths.

Something like this (hotplug-up.sh):

  #!/bin/bash

  echo 0 > /debug/sched_debug
  echo 1 > /debug/tracing/events/cpuhp/enable

  ALL_STATES=`cat /sys/devices/system/cpu/hotplug/states | cut -d':' -f1`
  STATES=${1:-$ALL_STATES}

  for state in $STATES
  do
	  echo 0 > /sys/devices/system/cpu/cpu1/online
	  echo 0 > /debug/tracing/trace
	  echo Fail state: $state
	  echo $state > /sys/devices/system/cpu/cpu1/hotplug/fail
	  cat /sys/devices/system/cpu/cpu1/hotplug/fail
	  echo 1 > /sys/devices/system/cpu/cpu1/online

	  cat /debug/tracing/trace > hotfail-${state}.trace

	  sleep 1
  done

Can be used to test for all possible rollback (barring multi-instance)
scenarios on CPU-up, CPU-down is a trivial modification of the above.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: bigeasy@linutronix.de
Cc: efault@gmx.de
Cc: rostedt@goodmis.org
Cc: max.byungchul.park@gmail.com
Link: https://lkml.kernel.org/r/20170920170546.972581715@infradead.org
parent 5ebe7742

include/linux/cpuhotplug.h

+2 −1
Original line number Diff line number Diff line
@@ -22,7 +22,8 @@ 
 */



enum cpuhp_state {

	CPUHP_OFFLINE,

	CPUHP_INVALID = -1,

	CPUHP_OFFLINE = 0,

	CPUHP_CREATE_THREADS,

	CPUHP_PERF_PREPARE,

	CPUHP_PERF_X86_PREPARE,

kernel/cpu.c

+59 −1
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ 
struct cpuhp_cpu_state {

	enum cpuhp_state	state;

	enum cpuhp_state	target;

	enum cpuhp_state	fail;

#ifdef CONFIG_SMP

	struct task_struct	*thread;

	bool			should_run;
@@ -67,7 +68,9 @@ struct cpuhp_cpu_state { 
#endif

};



static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);

static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {

	.fail = CPUHP_INVALID,

};



#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)

static struct lockdep_map cpuhp_state_up_map =
@@ -160,6 +163,15 @@ static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state, 
	int (*cb)(unsigned int cpu);

	int ret, cnt;



	if (st->fail == state) {

		st->fail = CPUHP_INVALID;



		if (!(bringup ? step->startup.single : step->teardown.single))

			return 0;



		return -EAGAIN;

	}



	if (!step->multi_instance) {

		WARN_ON_ONCE(lastp && *lastp);

		cb = bringup ? step->startup.single : step->teardown.single;
@@ -1805,9 +1817,55 @@ static ssize_t show_cpuhp_target(struct device *dev, 
}

static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);





static ssize_t write_cpuhp_fail(struct device *dev,

				struct device_attribute *attr,

				const char *buf, size_t count)

{

	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

	struct cpuhp_step *sp;

	int fail, ret;



	ret = kstrtoint(buf, 10, &fail);

	if (ret)

		return ret;



	/*

	 * Cannot fail STARTING/DYING callbacks.

	 */

	if (cpuhp_is_atomic_state(fail))

		return -EINVAL;



	/*

	 * Cannot fail anything that doesn't have callbacks.

	 */

	mutex_lock(&cpuhp_state_mutex);

	sp = cpuhp_get_step(fail);

	if (!sp->startup.single && !sp->teardown.single)

		ret = -EINVAL;

	mutex_unlock(&cpuhp_state_mutex);

	if (ret)

		return ret;



	st->fail = fail;



	return count;

}



static ssize_t show_cpuhp_fail(struct device *dev,

			       struct device_attribute *attr, char *buf)

{

	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);



	return sprintf(buf, "%d\n", st->fail);

}



static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);



static struct attribute *cpuhp_cpu_attrs[] = {

	&dev_attr_state.attr,

	&dev_attr_target.attr,

	&dev_attr_fail.attr,

	NULL

};

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