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[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: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Neil Brown 2006-10-17 00:10:35 -07:00 committed by Linus Torvalds
parent bea493a031
commit bd5349cfd2
1 changed files with 15 additions and 9 deletions
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24
kernel/cpu.c
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@ -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;