Message-ID: <20101104181606.GA3942@swordfish.minsk.epam.com>
Date:	Thu, 4 Nov 2010 20:16:06 +0200
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Roland McGrath <roland@...hat.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: task blocked for more than 120 seconds

On (11/04/10 18:32), Peter Zijlstra wrote:
> On Thu, 2010-11-04 at 17:19 +0100, Markus Trippelsdorf wrote:
> > On Thu, Nov 04, 2010 at 05:58:26PM +0200, Sergey Senozhatsky wrote:
> > > Hello,
> > > Got the following traces:
> > > 
> > > [42001.449295] INFO: task openbox:17761 blocked for more than 120 seconds.
> > > [42001.449303] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > [42001.449311] openbox       D 0000000000000003     0 17761   3723 0x00000000
> > > [42001.449321]  ffff88004ce8dc38 0000000000000046 0000000000000000 ffff88004ce8c000
> > > [42001.449333]  ffff88004ce8dfd8 0000000000012040 ffff880133010000 ffff88004ce8dfd8
> > > [42001.449343]  0000000000012040 0000000000012040 ffff88004ce8dfd8 0000000000012040
> > > [42001.449354] Call Trace:
> > > [42001.449369]  [<ffffffff814212ff>] schedule_timeout+0x38/0x220
> > > [42001.449381]  [<ffffffff81066f21>] ? mark_held_locks+0x50/0x72
> > > [42001.449389]  [<ffffffff81423dae>] ? _raw_spin_unlock_irq+0x2b/0x59
> > > [42001.449398]  [<ffffffff81036070>] ? get_parent_ip+0x11/0x41
> > > [42001.449406]  [<ffffffff81036132>] ? sub_preempt_count+0x92/0xa5
> > > [42001.449413]  [<ffffffff8142057e>] wait_for_common+0xca/0x144
> > > [42001.449421]  [<ffffffff81038b13>] ? default_wake_function+0x0/0xf
> > > [42001.449429]  [<ffffffff81423e4b>] ? _raw_spin_unlock_irqrestore+0x6f/0x74
> > > [42001.449436]  [<ffffffff81420692>] wait_for_completion+0x18/0x1a
> > > [42001.449445]  [<ffffffff81084808>] stop_one_cpu+0x8c/0xba
> > 
> > These traces look related to:
> > http://article.gmane.org/gmane.linux.kernel/1055100
> > 
> > Does reverting 34f971f6f7988be4d014eec3e3526bee6d007ffa help in your
> > case?
> 
>

Hello,
I'll test "sched: Fixup cross sched_class wakeup preemption" first
and then (if it fails) I'll test 34f971f6f7988be4d014eec3e3526bee6d007ffa 
revert.


	Sergey
 
> ---
> Subject: sched: Fixup cross sched_class wakeup preemption
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Sun Oct 31 12:37:04 CET 2010
> 
> Instead of dealing with sched classes inside each check_preempt_curr()
> implementation, pull out this logic into the generic wakeup preemption
> path.
> 
> This fixes a hang in KVM (and others) where we are waiting for the
> stop machine thread to run..
> 
> Tested-by: Marcelo Tosatti <mtosatti@...hat.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <new-submission>
> ---
>  kernel/sched.c          |   39 ++++++++++++++++++++++++++++-----------
>  kernel/sched_fair.c     |    6 ------
>  kernel/sched_stoptask.c |    2 +-
>  3 files changed, 29 insertions(+), 18 deletions(-)
> 
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -560,18 +560,9 @@ struct rq {
>  
>  static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
>  
> -static inline
> -void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
> -{
> -	rq->curr->sched_class->check_preempt_curr(rq, p, flags);
>  
> -	/*
> -	 * A queue event has occurred, and we're going to schedule.  In
> -	 * this case, we can save a useless back to back clock update.
> -	 */
> -	if (test_tsk_need_resched(p))
> -		rq->skip_clock_update = 1;
> -}
> +static inline
> +void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags);
>  
>  static inline int cpu_of(struct rq *rq)
>  {
> @@ -9400,4 +9391,30 @@ void synchronize_sched_expedited(void)
>  }
>  EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
>  
> +static inline
> +void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
> +{
> +	const struct sched_class *class;
> +
> +	if (p->sched_class == rq->curr->sched_class)
> +		rq->curr->sched_class->check_preempt_curr(rq, p, flags);
> +
> +	for_each_class(class) {
> +		if (class == rq->curr->sched_class)
> +			break;
> +		if (class == p->sched_class) {
> +			resched_task(rq->curr);
> +			break;
> +		}
> +	}
> +
> +	/*
> +	 * A queue event has occurred, and we're going to schedule.  In
> +	 * this case, we can save a useless back to back clock update.
> +	 */
> +	if (test_tsk_need_resched(rq->curr))
> +		rq->skip_clock_update = 1;
> +}
> +
> +
>  #endif /* #else #ifndef CONFIG_SMP */
> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -1654,12 +1654,6 @@ static void check_preempt_wakeup(struct
>  	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
>  	int scale = cfs_rq->nr_running >= sched_nr_latency;
>  
> -	if (unlikely(rt_prio(p->prio)))
> -		goto preempt;
> -
> -	if (unlikely(p->sched_class != &fair_sched_class))
> -		return;
> -
>  	if (unlikely(se == pse))
>  		return;
>  
> Index: linux-2.6/kernel/sched_stoptask.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_stoptask.c
> +++ linux-2.6/kernel/sched_stoptask.c
> @@ -19,7 +19,7 @@ select_task_rq_stop(struct rq *rq, struc
>  static void
>  check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
>  {
> -	resched_task(rq->curr); /* we preempt everything */
> +	/* we're never preempted */
>  }
>  
>  static struct task_struct *pick_next_task_stop(struct rq *rq)
> 

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