Commit bd5349cf authored by Neil Brown's avatar Neil Brown Committed by Linus Torvalds
Browse files

[PATCH] Convert cpu hotplug notifiers to use raw_notifier instead of blocking_notifier 



The use of blocking notifier by _cpu_up and _cpu_down in cpu.c has two
problem.

1/ An interaction with the workqueue notifier causes lockdep to spit a
   warning.

2/ A notifier could conceivable be added or removed while _cpu_up or
   _cpu_down are in process.  As each notifier is called twice (prepare
   then commit/abort) this could be unhealthy.

To fix to we simply take cpu_add_remove_lock while adding or removing
notifiers to/from the list.

This makes the 'blocking' usage unnecessary as all accesses to cpu_chain
are now protected by cpu_add_remove_lock.  So change "blocking" to "raw" in
all relevant places.  This fixes 1.

Credit: Andrew Morton
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com> (reporter)
Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent bea493a0

kernel/cpu.c

+15 −9
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ 
static DEFINE_MUTEX(cpu_add_remove_lock);

static DEFINE_MUTEX(cpu_bitmask_lock);



static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);

static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);



/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.

 * Should always be manipulated under cpu_add_remove_lock
@@ -68,7 +68,11 @@ EXPORT_SYMBOL_GPL(unlock_cpu_hotplug); 
/* Need to know about CPUs going up/down? */

int __cpuinit register_cpu_notifier(struct notifier_block *nb)

{

	return blocking_notifier_chain_register(&cpu_chain, nb);

	int ret;

	mutex_lock(&cpu_add_remove_lock);

	ret = raw_notifier_chain_register(&cpu_chain, nb);

	mutex_unlock(&cpu_add_remove_lock);

	return ret;

}



#ifdef CONFIG_HOTPLUG_CPU
@@ -77,7 +81,9 @@ EXPORT_SYMBOL(register_cpu_notifier); 


void unregister_cpu_notifier(struct notifier_block *nb)

{

	blocking_notifier_chain_unregister(&cpu_chain, nb);

	mutex_lock(&cpu_add_remove_lock);

	raw_notifier_chain_unregister(&cpu_chain, nb);

	mutex_unlock(&cpu_add_remove_lock);

}

EXPORT_SYMBOL(unregister_cpu_notifier);
@@ -126,7 +132,7 @@ static int _cpu_down(unsigned int cpu) 
	if (!cpu_online(cpu))

		return -EINVAL;



	err = blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,

	err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,

						(void *)(long)cpu);

	if (err == NOTIFY_BAD) {

		printk("%s: attempt to take down CPU %u failed\n",
@@ -146,7 +152,7 @@ static int _cpu_down(unsigned int cpu) 


	if (IS_ERR(p)) {

		/* CPU didn't die: tell everyone.  Can't complain. */

		if (blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,

		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,

				(void *)(long)cpu) == NOTIFY_BAD)

			BUG();
@@ -169,7 +175,7 @@ static int _cpu_down(unsigned int cpu) 
	put_cpu();



	/* CPU is completely dead: tell everyone.  Too late to complain. */

	if (blocking_notifier_call_chain(&cpu_chain, CPU_DEAD,

	if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD,

			(void *)(long)cpu) == NOTIFY_BAD)

		BUG();
@@ -206,7 +212,7 @@ static int __devinit _cpu_up(unsigned int cpu) 
	if (cpu_online(cpu) || !cpu_present(cpu))

		return -EINVAL;



	ret = blocking_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);

	ret = raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);

	if (ret == NOTIFY_BAD) {

		printk("%s: attempt to bring up CPU %u failed\n",

				__FUNCTION__, cpu);
@@ -223,11 +229,11 @@ static int __devinit _cpu_up(unsigned int cpu) 
	BUG_ON(!cpu_online(cpu));



	/* Now call notifier in preparation. */

	blocking_notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);

	raw_notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);



out_notify:

	if (ret != 0)

		blocking_notifier_call_chain(&cpu_chain,

		raw_notifier_call_chain(&cpu_chain,

				CPU_UP_CANCELED, hcpu);



	return ret;

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