Messages in this thread Patch in this message | | | Date | Fri, 7 Mar 2008 17:50:45 -0800 | From | Suresh Siddha <> | Subject | Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline |
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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@intel.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@intel.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); /* * Scan each rq for the lowest prio.
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