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SubjectThere is something with scheduler (was Re: [patch] Re: [regression bisect -next] BUG: using smp_processor_id() in preemptible [00000000] code: rmmod)
Hello, Ingo

Mike Galbraith's patch didn't work.

There is something with scheduler.

I still get this bug message:

BUG: using smp_processor_id() in preemptible [00000000] code: events/1/10
caller is vmstat_update+0x2a/0x3e
Pid: 10, comm: events/1 Not tainted 2.6.32-rc6-tip-01796-gd995f1d-dirty #118
Call Trace:
[<c02a3871>] debug_smp_processor_id+0xa5/0xbc
[<c01a229e>] vmstat_update+0x2a/0x3e
[<c014d6df>] worker_thread+0x134/0x1c2
[<c01a2274>] ? vmstat_update+0x0/0x3e
[<c0151361>] ? autoremove_wake_function+0x0/0x38
[<c014d5ab>] ? worker_thread+0x0/0x1c2
[<c0151298>] kthread+0x66/0x6e
[<c0151232>] ? kthread+0x0/0x6e
[<c0102e97>] kernel_thread_helper+0x7/0x10

Ftrace shows events/1 was run at cpu#0

<idle>-0 [000] 947.573031: set_next_entity <-pick_next_task_fair
<idle>-0 [000] 947.573032: update_stats_wait_end <-set_next_entity
<idle>-0 [000] 947.573033: __dequeue_entity <-set_next_entity
<idle>-0 [000] 947.573034: clear_buddies <-pick_next_task_fair
<idle>-0 [000] 947.573034: set_next_entity <-pick_next_task_fair
<idle>-0 [000] 947.573035: update_stats_wait_end <-set_next_entity
<idle>-0 [000] 947.573036: __dequeue_entity <-set_next_entity
<idle>-0 [000] 947.573037: hrtick_start_fair <-pick_next_task_fair
<idle>-0 [000] 947.573038: perf_event_task_sched_out <-schedule
<idle>-0 [000] 947.573039: memcpy <-tracing_record_cmdline
<idle>-0 [000] 947.573040: __switch_to <-schedule
events/1-10 [000] 947.573050: finish_task_switch <-schedule
events/1-10 [000] 947.573051: perf_event_task_sched_in <-finish_task_switch
events/1-10 [000] 947.573051: _spin_unlock_irq <-finish_task_switch
events/1-10 [000] 947.573052: finish_wait <-worker_thread
events/1-10 [000] 947.573053: kthread_should_stop <-worker_thread
events/1-10 [000] 947.573054: _spin_lock_irq <-worker_thread
events/1-10 [000] 947.573055: _spin_lock_irqsave <-probe_workqueue_execution
events/1-10 [000] 947.573056: _spin_unlock_irqrestore <-probe_workqueue_execution
events/1-10 [000] 947.573057: _spin_unlock_irq <-worker_thread
events/1-10 [000] 947.573058: flush_to_ldisc <-worker_thread
events/1-10 [000] 947.573059: tty_ldisc_ref <-flush_to_ldisc
events/1-10 [000] 947.573059: tty_ldisc_try <-tty_ldisc_ref
events/1-10 [000] 947.573060: _spin_lock_irqsave <-tty_ldisc_try
events/1-10 [000] 947.573061: _spin_unlock_irqrestore <-tty_ldisc_try


events/1 should run at cpu#1, but [000] shows it was run at cpu#0

events/1's cpus_allowed is correct:
# taskset -p 10
pid 10's current affinity mask: 2


Thanks
Lai

Mike Galbraith wrote:
> On Mon, 2009-11-02 at 19:28 +0100, Ingo Molnar wrote:
>> FYI, non-SMP builds broke:
>>
>> kernel/built-in.o: In function `kthread_bind':
>> (.text+0x1d328): undefined reference to `sched_kthread_bind'
>> make: *** [.tmp_vmlinux1] Error 1
>
> Oops. Outside the SMP block might work a little better.
>
> sched: Move the body of kthread_bind() to sched.c.
>
> Eric Paris reported that commit f685ceacab07d3f6c236f04803e2f2f0dbcc5afb
> causes boot time PREEMPT_DEBUG complaints.
>
> [ 4.590699] BUG: using smp_processor_id() in preemptible [00000000] code: rmmod/1314
> [ 4.593043] caller is task_hot+0x86/0xd0
> [ 4.593872] Pid: 1314, comm: rmmod Tainted: G W 2.6.32-rc3-fanotify #127
> [ 4.595443] Call Trace:
> [ 4.596177] [<ffffffff812ad35b>] debug_smp_processor_id+0x11b/0x120
> [ 4.597337] [<ffffffff81051d66>] task_hot+0x86/0xd0
> [ 4.598320] [<ffffffff81066275>] set_task_cpu+0x115/0x270
> [ 4.599368] [<ffffffff810985ab>] kthread_bind+0x6b/0x100
> [ 4.600354] [<ffffffff810914f0>] start_workqueue_thread+0x30/0x60
> [ 4.601545] [<ffffffff810941dd>] __create_workqueue_key+0x18d/0x2f0
> [ 4.602526] [<ffffffff810d9bee>] stop_machine_create+0x4e/0xd0
> [ 4.603811] [<ffffffff810c5818>] sys_delete_module+0x98/0x250
> [ 4.604922] [<ffffffff810e2505>] ? audit_syscall_entry+0x205/0x290
> [ 4.606202] [<ffffffff81013202>] system_call_fastpath+0x16/0x1b
>
> Since kthread_bind() messes with scheduler internals, move the body to sched.c,
> and lock the runqueue.
>
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Reported-by: Eric Paris <eparis@redhat.com>
> LKML-Reference: <new-submission>
>
> ---
> kernel/kthread.c | 15 ++++++---------
> kernel/sched.c | 31 +++++++++++++++++++++++++++++++
> 2 files changed, 37 insertions(+), 9 deletions(-)
>
> Index: linux-2.6/kernel/kthread.c
> ===================================================================
> --- linux-2.6.orig/kernel/kthread.c
> +++ linux-2.6/kernel/kthread.c
> @@ -149,6 +149,8 @@ struct task_struct *kthread_create(int (
> }
> EXPORT_SYMBOL(kthread_create);
>
> +extern void sched_kthread_bind(struct task_struct *k, unsigned int cpu);
> +
> /**
> * kthread_bind - bind a just-created kthread to a cpu.
> * @k: thread created by kthread_create().
> @@ -157,18 +159,13 @@ EXPORT_SYMBOL(kthread_create);
> * Description: This function is equivalent to set_cpus_allowed(),
> * except that @cpu doesn't need to be online, and the thread must be
> * stopped (i.e., just returned from kthread_create()).
> + *
> + * The runqueue must be locked, ergo move the body if this function
> + * to sched.c
> */
> void kthread_bind(struct task_struct *k, unsigned int cpu)
> {
> - /* Must have done schedule() in kthread() before we set_task_cpu */
> - if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
> - WARN_ON(1);
> - return;
> - }
> - set_task_cpu(k, cpu);
> - k->cpus_allowed = cpumask_of_cpu(cpu);
> - k->rt.nr_cpus_allowed = 1;
> - k->flags |= PF_THREAD_BOUND;
> + sched_kthread_bind(k, cpu);
> }
> EXPORT_SYMBOL(kthread_bind);
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -1992,6 +1992,37 @@ static inline void check_class_changed(s
> p->sched_class->prio_changed(rq, p, oldprio, running);
> }
>
> +/**
> + * sched_kthread_bind - bind a just-created kthread to a cpu.
> + * @k: thread created by kthread_create().
> + * @cpu: cpu (might not be online, must be possible) for @k to run on.
> + *
> + * Description: This function is equivalent to set_cpus_allowed(),
> + * except that @cpu doesn't need to be online, and the thread must be
> + * stopped (i.e., just returned from kthread_create()).
> + *
> + * Function lives here instead of kthread.c because it messes with
> + * scheduler internals which require locking.
> + */
> +void sched_kthread_bind(struct task_struct *p, unsigned int cpu)
> +{
> + struct rq *rq = cpu_rq(cpu);
> + unsigned long flags;
> +
> + /* Must have done schedule() in kthread() before we set_task_cpu */
> + if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
> + WARN_ON(1);
> + return;
> + }
> +
> + spin_lock_irqsave(&rq->lock, flags);
> + set_task_cpu(p, cpu);
> + p->cpus_allowed = cpumask_of_cpu(cpu);
> + p->rt.nr_cpus_allowed = 1;
> + p->flags |= PF_THREAD_BOUND;
> + spin_unlock_irqrestore(&rq->lock, flags);
> +}
> +
> #ifdef CONFIG_SMP
> /*
> * Is this task likely cache-hot:
>
>
> --
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