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Message-ID: <17711.6883.764895.822786@cse.unsw.edu.au>
Date: Fri, 13 Oct 2006 14:49:39 +1000
From: Neil Brown <neilb@...e.de>
To: Andrew Morton <akpm@...l.org>
Cc: Arjan van de Ven <arjan@...radead.org>,
Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
rusty@...tcorp.com.au
Subject: Re: _cpu_down deadlock [was Re: 2.6.19-rc1-mm1]
On Thursday October 12, akpm@...l.org wrote:
> On Thu, 12 Oct 2006 17:53:11 +1000
> Neil Brown <neilb@...e.de> wrote:
>
> > I think I'm in favour of the following.
>
> Would be simpler to take cpu_add_remove_lock in
> [un]register_cpu_notifier(). I actually thought I'd done that to fix this
> bug but must have forgotten or lost the patch :(
>
> We can then convert all the notifier chains in there to raw_*.
The two philosophers gaped at him.
"Bloody hell," said Majikthise, "now that is what I call
thinking. Here Vroomfondel, why do we never think of things like
that?"
"Dunno," said Vroomfondel in an awed whisper, "think our brains must
be too highly trained Majikthise."
[ http://flag.blackened.net/dinsdale/dna/book1.html ]
I guess you'll be wanting this then, unless you have done it already.
NeilBrown
-----------
Subject: 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@...tcorp.com.au (maintainer)
Cc: Michal Piotrowski <michal.k.k.piotrowski@...il.com> (reporter)
Signed-off-by: Neil Brown <neilb@...e.de>
### Diffstat output
./kernel/cpu.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff .prev/kernel/cpu.c ./kernel/cpu.c
--- .prev/kernel/cpu.c 2006-10-13 14:30:56.000000000 +1000
+++ ./kernel/cpu.c 2006-10-13 14:33:49.000000000 +1000
@@ -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 in
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 in
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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