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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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