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Date: Mon, 23 Nov 2009 15:23:43 +0530
From: Sachin Sant <sachinp@...ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: ego@...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!
Peter Zijlstra wrote:
> 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:
>
Peter i still can recreate this issue with today's next(20091123).
Looks like the following patch haven't been merged yet.
Thanks
-Sachin
> ---
> 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;
> }
> }
>
>
>
>
--
---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
---------------------------------
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