From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xensource.com,
julie Sullivan <kernelmail.jms@gmail.com>,
linux-kernel@vger.kernel.org, chengxu@linux.vnet.ibm.com
Subject: Re: PROBLEM: 3.0-rc kernels unbootable since -rc3
Date: Tue, 12 Jul 2011 09:39:47 -0700 [thread overview]
Message-ID: <20110712163947.GF2326@linux.vnet.ibm.com> (raw)
In-Reply-To: <20110712160324.GA1186@dumpdata.com>
On Tue, Jul 12, 2011 at 12:03:24PM -0400, Konrad Rzeszutek Wilk wrote:
> > > http://darnok.org/xen/cpu1.log
> >
> > OK, a fair amount of variety, then lots and lots of task_waking_fair(),
> > so I still feel good about asking you for the following.
> .. snup..
> > Hmmm... Given that this is persisting for many many seconds, it might
> > be better to check for at least 10,000,000 passes. In contrast, 1000
> > passes might elapse just waiting for a cache miss to complete.
>
> Changed it to that large number. This is the diff I used:
>
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 433491c..e185c04 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1392,14 +1392,19 @@ static void task_waking_fair(struct task_struct *p)
> struct sched_entity *se = &p->se;
> struct cfs_rq *cfs_rq = cfs_rq_of(se);
> u64 min_vruntime;
> + u64 loop_cnt = 0UL;
>
> #ifndef CONFIG_64BIT
> u64 min_vruntime_copy;
> -
> + loop_cnt = 0UL;
> do {
> min_vruntime_copy = cfs_rq->min_vruntime_copy;
> smp_rmb();
> min_vruntime = cfs_rq->min_vruntime;
> + if (loop_cnt++ > 10000000) {
> + printk(KERN_INFO "POKE!\n");
> + loop_cnt = 0UL;
> + }
> } while (min_vruntime != min_vruntime_copy);
> #else
> min_vruntime = cfs_rq->min_vruntime;
>
> And the log is:
> http://darnok.org/xen/loop_cnt.log
>
> which seems to imply that we are indeed stuck in that loop
> forever.
It does indeed, thank you! Also it looks like interrupts are
disabled, and that timekeeping is similarly out of action.
> > Other possible causes include:
>
> What is really strange is that I can only reproduce this on 32-bit builds.
Not strange at all. If you have a 64-bit build, the function doesn't
have a loop. ;-)
> > o A mismatch between Xen's and RCU's ideas of how CONFIG_NO_HZ
> > works. If Xen thinks that the CPU is in CONFIG_NO_HZ's
> > dyntick-idle mode, but RCU thinks otherwise, the grace period
> > might stall.
>
> One sure way to figure this out is to disable CONFIG_NO_HZ right?
> Or will that take away task_waking_fair case as well?
Disabling CONFIG_NO_HZ would be an interesting test case.
> > o Problems due to portions of the code attempting to use
> > RCU read-side critical sections while in dyntick-idle mode.
> > Frederic Weisbecker has located some of these, (though not yet
> > in Xen) and he has some diagnositics which may be found at:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git
> >
> > on branch eqscheck.2011.07.08a.
> >
> > You need to enable CONFIG_PROVE_RCU for these diagnostics to
> > be executed.
>
> Ok, let me try those too.
Thank you!
> > o As always, there might be bugs in RCU. ;-)
> >
> > But the loop in task_waking_fair() looks like the most prominent smoking
> > gun at the moment.
And could you also please try out the patch that I posted earlier?
Thaxn, Paul
next prev parent reply other threads:[~2011-07-12 17:22 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-06 21:10 PROBLEM: 3.0-rc kernels unbootable since -rc3 julie Sullivan
2011-07-06 21:23 ` Paul E. McKenney
2011-07-07 19:31 ` Paul E. McKenney
2011-07-07 19:47 ` julie Sullivan
2011-07-07 19:58 ` Paul E. McKenney
2011-07-07 20:28 ` julie Sullivan
2011-07-07 20:47 ` julie Sullivan
2011-07-08 0:29 ` Paul E. McKenney
2011-07-09 10:09 ` Paul E. McKenney
2011-07-10 0:45 ` julie Sullivan
2011-07-10 3:25 ` Paul E. McKenney
2011-07-10 16:38 ` julie Sullivan
2011-07-10 17:16 ` Paul E. McKenney
2011-07-10 17:35 ` Paul E. McKenney
2011-07-10 20:30 ` julie Sullivan
2011-07-10 21:46 ` Paul E. McKenney
2011-07-10 21:50 ` julie Sullivan
2011-07-10 23:14 ` Paul E. McKenney
2011-07-11 16:24 ` Konrad Rzeszutek Wilk
2011-07-11 17:13 ` Paul E. McKenney
2011-07-11 19:30 ` Konrad Rzeszutek Wilk
2011-07-11 20:15 ` Paul E. McKenney
2011-07-11 21:09 ` Konrad Rzeszutek Wilk
2011-07-12 10:55 ` Paul E. McKenney
2011-07-12 14:12 ` Konrad Rzeszutek Wilk
2011-07-12 14:49 ` Paul E. McKenney
2011-07-12 15:07 ` Paul E. McKenney
2011-07-12 15:15 ` Paul E. McKenney
2011-07-12 15:22 ` Paul E. McKenney
2011-07-12 16:32 ` PROBLEM: 3.0-rc kernels unbootable since -rc3 - under Xen, 32-bit guest only Konrad Rzeszutek Wilk
2011-07-12 16:46 ` Paul E. McKenney
2011-07-12 16:03 ` PROBLEM: 3.0-rc kernels unbootable since -rc3 Konrad Rzeszutek Wilk
2011-07-12 16:39 ` Paul E. McKenney [this message]
2011-07-12 18:01 ` Konrad Rzeszutek Wilk
2011-07-12 18:59 ` Paul E. McKenney
2011-07-12 19:07 ` Konrad Rzeszutek Wilk
2011-07-12 20:52 ` Paul E. McKenney
2011-07-12 19:10 ` Peter Zijlstra
2011-07-12 19:57 ` Konrad Rzeszutek Wilk
2011-07-12 20:46 ` Paul E. McKenney
2011-07-12 21:04 ` Julie Sullivan
2011-07-12 21:07 ` Paul E. McKenney
2011-07-12 20:05 ` Paul E. McKenney
2011-07-12 6:33 ` [Xen-devel] " Sander Eikelenboom
2011-07-12 14:05 ` Paul E. McKenney
[not found] ` <CAAVPGOMSprJSkzziH6hJv9PweOONzsMaRZEK2ZSrV3xFBReTPw@mail.gmail.com>
[not found] ` <20110711214301.GP2245@linux.vnet.ibm.com>
2011-07-12 21:15 ` Julie Sullivan
2011-07-12 21:29 ` Paul E. McKenney
2011-07-12 21:35 ` Julie Sullivan
2011-07-12 21:49 ` Julie Sullivan
2011-07-12 22:00 ` Paul E. McKenney
2011-07-13 7:18 ` RKK
2011-07-13 15:47 ` Paul E. McKenney
2011-07-13 20:57 ` Julie Sullivan
2011-07-13 21:23 ` Paul E. McKenney
2011-07-07 17:28 ` julie Sullivan
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