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Date: Fri, 13 Nov 2009 11:31:21 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: ego@...ibm.com
Cc: Sachin Sant <sachinp@...ibm.com>,
LKML <linux-kernel@...r.kernel.org>,
Stephen Rothwell <sfr@...b.auug.org.au>,
linux-next@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Mike Galbraith <efault@....de>
Subject: Re: -next: Nov 12 - kernel BUG at kernel/sched.c:7359!
On Fri, 2009-11-13 at 11:16 +0100, Peter Zijlstra wrote:
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -2376,7 +2376,15 @@ static int try_to_wake_up(struct task_st
> p->state = TASK_WAKING;
> __task_rq_unlock(rq);
>
> +again:
> cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
> + if (!cpu_online(cpu))
> + cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);
> + if (cpu >= nr_cpu_ids) {
> + cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
> + goto again;
> + }
> +
> if (cpu != orig_cpu) {
> rq = cpu_rq(cpu);
> update_rq_clock(rq);
>
> is what I stuck in and am compiling now.. we'll see what that does.
Well, it boots for me, but then, I've not been able to reproduce any
issues anyway :/
/me goes try a PREEMPT=n kernel, since that is what Mike reports boot
funnies with..
Full running diff against -tip:
---
diff --git a/kernel/sched.c b/kernel/sched.c
index 1f2e99d..7089063 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2374,17 +2374,24 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
if (task_contributes_to_load(p))
rq->nr_uninterruptible--;
p->state = TASK_WAKING;
- task_rq_unlock(rq, &flags);
+ __task_rq_unlock(rq);
+again:
cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
+ if (!cpu_online(cpu))
+ cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);
+ if (cpu >= nr_cpu_ids) {
+ printk(KERN_ERR "Breaking affinity on %d/%s\n", p->pid, p->comm);
+ cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
+ goto again;
+ }
+
if (cpu != orig_cpu) {
- local_irq_save(flags);
rq = cpu_rq(cpu);
update_rq_clock(rq);
set_task_cpu(p, cpu);
- local_irq_restore(flags);
}
- rq = task_rq_lock(p, &flags);
+ rq = __task_rq_lock(p);
WARN_ON(p->state != TASK_WAKING);
cpu = task_cpu(p);
@@ -7620,6 +7627,8 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
unsigned long flags;
struct rq *rq;
+ printk(KERN_ERR "migration call\n");
+
switch (action) {
case CPU_UP_PREPARE:
@@ -9186,6 +9195,8 @@ int __init sched_create_sysfs_power_savings_entries(struct sysdev_class *cls)
static int update_sched_domains(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
+ printk(KERN_ERR "update_sched_domains\n");
+
switch (action) {
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5488a5d..0ff21af 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1345,6 +1345,37 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
}
/*
+ * Try and locate an idle CPU in the sched_domain.
+ */
+static int
+select_idle_sibling(struct task_struct *p, struct sched_domain *sd, int target)
+{
+ int cpu = smp_processor_id();
+ int prev_cpu = task_cpu(p);
+ int i;
+
+ /*
+ * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
+ * test in select_task_rq_fair) and the prev_cpu is idle then that's
+ * always a better target than the current cpu.
+ */
+ if (target == cpu && !cpu_rq(prev_cpu)->cfs.nr_running)
+ return prev_cpu;
+
+ /*
+ * Otherwise, iterate the domain and find an elegible idle cpu.
+ */
+ for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
+ if (!cpu_rq(i)->cfs.nr_running) {
+ target = i;
+ break;
+ }
+ }
+
+ return target;
+}
+
+/*
* sched_balance_self: balance the current task (running on cpu) in domains
* that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
* SD_BALANCE_EXEC.
@@ -1398,37 +1429,34 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
want_sd = 0;
}
- if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
- int candidate = -1, i;
+ /*
+ * While iterating the domains looking for a spanning
+ * WAKE_AFFINE domain, adjust the affine target to any idle cpu
+ * in cache sharing domains along the way.
+ */
+ if (want_affine) {
+ int target = -1;
+ /*
+ * If both cpu and prev_cpu are part of this domain,
+ * cpu is a valid SD_WAKE_AFFINE target.
+ */
if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
- candidate = cpu;
+ target = cpu;
/*
- * Check for an idle shared cache.
+ * If there's an idle sibling in this domain, make that
+ * the wake_affine target instead of the current cpu.
*/
- if (tmp->flags & SD_PREFER_SIBLING) {
- if (candidate == cpu) {
- if (!cpu_rq(prev_cpu)->cfs.nr_running)
- candidate = prev_cpu;
- }
+ if (tmp->flags & SD_PREFER_SIBLING)
+ target = select_idle_sibling(p, tmp, target);
- if (candidate == -1 || candidate == cpu) {
- for_each_cpu(i, sched_domain_span(tmp)) {
- if (!cpumask_test_cpu(i, &p->cpus_allowed))
- continue;
- if (!cpu_rq(i)->cfs.nr_running) {
- candidate = i;
- break;
- }
- }
+ if (target >= 0) {
+ if (tmp->flags & SD_WAKE_AFFINE) {
+ affine_sd = tmp;
+ want_affine = 0;
}
- }
-
- if (candidate >= 0) {
- affine_sd = tmp;
- want_affine = 0;
- cpu = candidate;
+ cpu = target;
}
}
--
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