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Date: Sat, 08 Mar 2008 00:10:15 -0500
From: Gregory Haskins <ghaskins@...ell.com>
To: suresh.b.siddha@...el.com
Cc: rjw@...k.pl, akpm@...ux-foundation.org, dmitry.adamushko@...il.com,
ego@...ibm.com, mingo@...e.hu, oleg@...sign.ru,
yi.y.yang@...el.com, linux-kernel@...r.kernel.org,
tglx@...utronix.de, ghaskins@...ell.com
Subject: [PATCH] adjust root-domain->online span in response to hotplug event
Suresh Siddha wrote:
> On Sat, Mar 08, 2008 at 12:43:15AM +0100, Rafael J. Wysocki wrote:
>> On Saturday, 8 of March 2008, Andrew Morton wrote:
>>> On Fri, 7 Mar 2008 15:01:26 -0800
>>> Suresh Siddha <suresh.b.siddha@...el.com> wrote:
>>>
>>>> Andrew, Please check if the appended patch fixes your power-off
problem aswell.
>>>> ...
>>>>
>>>> --- a/kernel/sched.c
>>>> +++ b/kernel/sched.c
>>>> @@ -5882,6 +5882,7 @@ migration_call(struct notifier_block *nfb,
unsigned long action, void *hcpu)
>>>> break;
>>>>
>>>> case CPU_DOWN_PREPARE:
>>>> + case CPU_DOWN_PREPARE_FROZEN:
>>>> /* Update our root-domain */
>>>> rq = cpu_rq(cpu);
>>>> spin_lock_irqsave(&rq->lock, flags);
>>> No, it does not.
>> Well, this is a bug nevertheless.
>>
>
> Well, my previous root cause needs some small changes.
>
> During the notifier call chain for CPU_DOWN(till 'update_sched_domains'
> is called atleast), all the cpu's are attached to 'def_root_domain',
for whom
> online mask still has the offline cpu.
>
> This is because, during CPU_DOWN_PREPARE, migration_call() first clears
> the root_domain->online, and later during the DOWN_PREPARE call chain
> detach_destroy_domains() attach to def_root_domain with
cpu_online_map(which
> still has the just about to die 'cpu' set).
>
> So essentially, during the notifier call chain of CPU_DOWN (before
> 'update_sched_domains' is called atleast), any one doing RT process
> wakeup's (for example: kthread_stop()) can still end up on the dead cpu.
>
> Andrew, Can you please try one more patch(appended) to see if it helps?
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index 0a6d2e5..8cb707c 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -597,7 +597,7 @@ static int find_lowest_cpus(struct task_struct
*task, cpumask_t *lowest_mask)
> int count = 0;
> int cpu;
>
> - cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed);
> + cpus_and(*lowest_mask, task->cpus_allowed, cpu_online_map);
>
> /*
Hi Suresh,
Unfortunately, this patch will introduce its own set of bugs.
However, your analysis was spot-on. I think I see the problem now. It
was introduced when I put a hack in to "fix" s2ram problems in -mm as a
result of the new root-domain logic. I think the following patch will
fix both issues:
(I verified that I could take a cpu offline/online, but I don't have an
s2ram compatible machine handy. Andrew, I believe you could reproduce
the s2ram problem a few months ago when that issue popped up. So if you
could, please verify that s2ram also works with this patch applied, in
addition to the hotplug problem.
Regards,
-Greg
-------------------------------------------------
adjust root-domain->online span in response to hotplug event
We currently set the root-domain online span automatically when the domain
is added to the cpu if the cpu is already a member of cpu_online_map.
This was done as a hack/bug-fix for s2ram, but it also causes a problem
with hotplug CPU_DOWN transitioning. The right way to fix the original
problem is to actually respond to CPU_UP events, instead of CPU_ONLINE,
which is already too late.
Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
---
kernel/sched.c | 18 +++++++-----------
1 files changed, 7 insertions(+), 11 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 52b9867..b02e4fc 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5813,6 +5813,13 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
/* Must be high prio: stop_machine expects to yield to it. */
rq = task_rq_lock(p, &flags);
__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
+
+ /* Update our root-domain */
+ if (rq->rd) {
+ BUG_ON(!cpu_isset(cpu, rq->rd->span));
+ cpu_set(cpu, rq->rd->online);
+ }
+
task_rq_unlock(rq, &flags);
cpu_rq(cpu)->migration_thread = p;
break;
@@ -5821,15 +5828,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
case CPU_ONLINE_FROZEN:
/* Strictly unnecessary, as first user will wake it. */
wake_up_process(cpu_rq(cpu)->migration_thread);
-
- /* Update our root-domain */
- rq = cpu_rq(cpu);
- spin_lock_irqsave(&rq->lock, flags);
- if (rq->rd) {
- BUG_ON(!cpu_isset(cpu, rq->rd->span));
- cpu_set(cpu, rq->rd->online);
- }
- spin_unlock_irqrestore(&rq->lock, flags);
break;
#ifdef CONFIG_HOTPLUG_CPU
@@ -6105,8 +6103,6 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
rq->rd = rd;
cpu_set(rq->cpu, rd->span);
- if (cpu_isset(rq->cpu, cpu_online_map))
- cpu_set(rq->cpu, rd->online);
for (class = sched_class_highest; class; class = class->next) {
if (class->join_domain)
--
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