Subject: Re: linux-next: Tree for April 14 (Call-traces: RCU/ACPI/WQ related?)

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 26 Apr 2011 08:42:55 -0700

On Tue, Apr 26, 2011 at 02:50:25PM +0200, Sedat Dilek wrote:
> On Tue, Apr 26, 2011 at 2:42 PM, Paul E. McKenney
> <[email-masked]> wrote:
> > On Tue, Apr 26, 2011 at 01:45:31PM +0200, Sedat Dilek wrote:
> >> On Tue, Apr 26, 2011 at 7:06 AM, Paul E. McKenney
> >> <[email-masked]> wrote:
> >> > On Sun, Apr 24, 2011 at 09:43:31AM -0700, Paul E. McKenney wrote:
> >> >> On Sun, Apr 24, 2011 at 11:36:44AM +0200, Sedat Dilek wrote:
> >> >> > On Sun, Apr 24, 2011 at 8:27 AM, Paul E. McKenney
> >> >> > <[email-masked]> wrote:
> >> >>
> >> >> [ . . . ]
> >> >>
> >> >> > > OK, this looks unrelated, but just in case, could you please try it
> >> >> > > again with the following patch?  (Not mainlinable, debug only.)
> >> >> > >
> >> >> > > Also, it does look like you are still seeing a grace-period hang.
> >> >> > > Could you please send the output of the script?  Same one as last time.
> >> >> > >
> >> >> > >                                                        Thanx, Paul
> >> >> > >
> >> >> > > ------------------------------------------------------------------------
> >> >> > >
> >> >> > >  debugobjects.c |    8 +++++---
> >> >> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> >> >> > >
> >> >> > > diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> >> >> > > index 9d86e45..10a7c7a 100644
> >> >> > > --- a/lib/debugobjects.c
> >> >> > > +++ b/lib/debugobjects.c
> >> >> > > @@ -289,10 +289,12 @@ static void debug_object_is_on_stack(void *addr, int onstack)
> >> >> > >                return;
> >> >> > >
> >> >> > >        limit++;
> >> >> > > -       if (is_on_stack)
> >> >> > > +       if (is_on_stack) {
> >> >> > > +               struct rcu_head *p = (struct rcu_head *)addr;
> >> >> > >                printk(KERN_WARNING
> >> >> > > -                      "ODEBUG: object is on stack, but not annotated\n");
> >> >> > > -       else
> >> >> > > +                      "ODEBUG: object is on stack, but not annotated: %p\n",
> >> >> > > +                      p->func);
> >> >> > > +       } else
> >> >> > >                printk(KERN_WARNING
> >> >> > >                       "ODEBUG: object is not on stack, but annotated\n");
> >> >> > >        WARN_ON(1);
> >> >> > >
> >> >> >
> >> >> > Somehow your attached patch was not applicable.
> >> >> > As the changes were a few lines I applied it by myself.
> >> >> > Attached are log, dmesg and patches (orig + mine)
> >> >>
> >> >> Hmmm...  Does 0xc10231a1 correspond to a function in your build?  If so,
> >> >> could you please let me know which one?
> >> >>
> >> >> OK, so according to "ps" the per-CPU kthread is runnable, but it appears
> >> >> to never run.  You only have one CPU, so it cannot be waiting due to
> >> >> running on the wrong CPU.  The only other loop is in wait_event(), and
> >> >> that code looks good -- besides, if wait_event() was broken, we would
> >> >> be seeing breakage everywhere.
> >> >>
> >> >> Peter, any thoughts on what I might have done wrong to get the scheduler
> >> >> into a state where it was ignoring a runnable realtime task?
> >> >
> >> > Hello, Sedat,
> >> >
> >> > Here is a diagnostic patch to apply on top of sedat.2011.04.23a from
> >> > the -rcu git tree.  Could you please try it out, let me know what
> >> > happens, and run the last collectdebugfs.sh during the test?
> >> >
> >> >                                                        Thanx, Paul
> >> >
> >> > ------------------------------------------------------------------------
> >> >
> >> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> >> > index 6cf6e47..65ae701 100644
> >> > --- a/kernel/rcutree.c
> >> > +++ b/kernel/rcutree.c
> >> > @@ -1524,9 +1524,9 @@ static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
> >> >                return;
> >> >        if (to_rt) {
> >> >                policy = SCHED_NORMAL;
> >> > -               sp.sched_priority = RCU_KTHREAD_PRIO;
> >> > +               sp.sched_priority = 0;
> >> >        } else {
> >> > -               policy = SCHED_FIFO;
> >> > +               policy = SCHED_NORMAL;
> >> >                sp.sched_priority = 0;
> >> >        }
> >> >        sched_setscheduler_nocheck(t, policy, &sp);
> >> > @@ -1566,8 +1566,8 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
> >> >        sp.sched_priority = 0;
> >> >        sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
> >> >        schedule();
> >> > -       sp.sched_priority = RCU_KTHREAD_PRIO;
> >> > -       sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
> >> > +       sp.sched_priority = 0;
> >> > +       sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
> >> >        del_timer(&yield_timer);
> >> >  }
> >> >
> >> > @@ -1671,8 +1671,8 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
> >> >        WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
> >> >        per_cpu(rcu_cpu_kthread_task, cpu) = t;
> >> >        wake_up_process(t);
> >> > -       sp.sched_priority = RCU_KTHREAD_PRIO;
> >> > -       sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> >> > +       sp.sched_priority = 0;
> >> > +       sched_setscheduler_nocheck(t, SCHED_NORMAL, &sp);
> >> >        return 0;
> >> >  }
> >> >
> >> > @@ -1713,8 +1713,8 @@ static int rcu_node_kthread(void *arg)
> >> >                                continue;
> >> >                        }
> >> >                        per_cpu(rcu_cpu_has_work, cpu) = 1;
> >> > -                       sp.sched_priority = RCU_KTHREAD_PRIO;
> >> > -                       sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> >> > +                       sp.sched_priority = 0;
> >> > +                       sched_setscheduler_nocheck(t, SCHED_NORMAL, &sp);
> >> >                        preempt_enable();
> >> >                }
> >> >        }
> >> > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> >> > index a21413d..baee185 100644
> >> > --- a/kernel/rcutree_plugin.h
> >> > +++ b/kernel/rcutree_plugin.h
> >> > @@ -1307,8 +1307,8 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
> >> >        rnp->boost_kthread_task = t;
> >> >        raw_spin_unlock_irqrestore(&rnp->lock, flags);
> >> >        wake_up_process(t);
> >> > -       sp.sched_priority = RCU_KTHREAD_PRIO;
> >> > -       sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> >> > +       sp.sched_priority = 0;
> >> > +       sched_setscheduler_nocheck(t, SCHED_NORMAL, &sp);
> >> >        return 0;
> >> >  }
> >> >
> >> >
> >>
> >> Hi Paul,
> >>
> >> I have tested with your patch and kept the kernel-config file from
> >> previous tests (don't get confused by the new name).
> >> Hope this helps you.
> >>
> >> I have some questions to k-c options espcially X86_UP and
> >> CONFIG_RCU_FANOUT=32 options.
> >> To what extent can they influence our RCU issue?
> >> The below options were not set for this round of testing, but I would
> >> like to have a feedback.
> >> Thanks in advance.
> >>
> >> Would these settings be more optimal for a UP-machine?
> >>
> >> # CONFIG_SMP is not set
> >> # CONFIG_M486 is not set
> >> CONFIG_M686=y
> >> CONFIG_NR_CPUS=1
> >
> > These should be fine.
> >
> >> CONFIG_X86_UP_APIC=y
> >> CONFIG_X86_UP_IOAPIC=y
> >
> > These I don't know about.
> >
> >> CONFIG_HIGHMEM4G=y
> >
> > This one seems good for allowing the system to go as long as possible.
> >
> >> Is CONFIG_RCU_FANOUT=32 OK?
> >
> > On a UP system, this one doesn't matter.
> >
> >> With reverting commit 687d7a960aea46e016182c7ce346d62c4dbd0366 ("rcu:
> >> restrict TREE_RCU to SMP builds with !PREEMPT").
> >
> > Thank you for trying this one out!
> >
> > I don't see any sign of a grace-period hang.  Did your test complete
> > correctly?
> >
> >                                                        Thanx, Paul
> >
> 
> Thanks for the comments.
> 
> I let run the script very long (approx. one hour) and did parallelly
> my daily work.
> Then booted into a known as working kernel.
> Did I miss something, should I stress more?

I wouldn't know -- I never have been able to reproduce this.

For the moment, I will do my inspections assuming that the bug
has something to do with realtime priority.

Thank you again for your testing!

							Thanx, Paul