From: Juri Lelli <juri.lelli@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Juri Lelli <juri.lelli@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
syzbot <syzbot+385468161961cee80c31@syzkaller.appspotmail.com>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
LKML <linux-kernel@vger.kernel.org>,
mingo@redhat.com, nstange@suse.de,
syzkaller-bugs@googlegroups.com
Subject: Re: INFO: rcu detected stall in do_idle
Date: Tue, 16 Oct 2018 17:36:08 +0200 [thread overview]
Message-ID: <20181016153608.GH9130@localhost.localdomain> (raw)
In-Reply-To: <alpine.DEB.2.21.1810161643540.7787@nanos.tec.linutronix.de>
On 16/10/18 16:45, Thomas Gleixner wrote:
> On Tue, 16 Oct 2018, Juri Lelli wrote:
> > On 16/10/18 16:03, Peter Zijlstra wrote:
> > > On Tue, Oct 16, 2018 at 03:24:06PM +0200, Thomas Gleixner wrote:
> > > > It does reproduce here but with a kworker stall. Looking at the reproducer:
> > > >
> > > > *(uint32_t*)0x20000000 = 0;
> > > > *(uint32_t*)0x20000004 = 6;
> > > > *(uint64_t*)0x20000008 = 0;
> > > > *(uint32_t*)0x20000010 = 0;
> > > > *(uint32_t*)0x20000014 = 0;
> > > > *(uint64_t*)0x20000018 = 0x9917;
> > > > *(uint64_t*)0x20000020 = 0xffff;
> > > > *(uint64_t*)0x20000028 = 0;
> > > > syscall(__NR_sched_setattr, 0, 0x20000000, 0);
> > > >
> > > > which means:
> > > >
> > > > struct sched_attr {
> > > > .size = 0,
> > > > .policy = 6,
> > > > .flags = 0,
> > > > .nice = 0,
> > > > .priority = 0,
> > > > .deadline = 0x9917,
> > > > .runtime = 0xffff,
> > > > .period = 0,
> > > > }
> > > >
> > > > policy 6 is SCHED_DEADLINE
> > > >
> > > > That makes the thread hog the CPU and prevents all kind of stuff to run.
> > > >
> > > > Peter, is that expected behaviour?
> > >
> > > Sorta, just like FIFO-99 while(1);. Except we should be rejecting the
> > > above configuration, because of the rule:
> > >
> > > runtime <= deadline <= period
> > >
> > > Juri, where were we supposed to check that?
> >
> > Not if period == 0.
> >
> > https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2632
> > https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2515
> >
> > Now, maybe we should be checking also against the default 95% cap?
>
> If the cap is active, then yes. But you want to use the actual
> configuration not the default.
Sure.
Although DEADLINE bandwidth is "replicated" across the CPUs of a domain,
so we can still admit a while(1) on multi-CPUs domains. Mmm, guess we
should be able to fix this however if we limit also the per-task maximum
bandwidth considering rt_runtime/rt_period.
next prev parent reply other threads:[~2018-10-16 15:36 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-13 7:31 INFO: rcu detected stall in do_idle syzbot
2018-10-16 13:24 ` Thomas Gleixner
2018-10-16 14:03 ` Peter Zijlstra
2018-10-16 14:41 ` Juri Lelli
2018-10-16 14:45 ` Thomas Gleixner
2018-10-16 15:36 ` Juri Lelli [this message]
2018-10-18 8:28 ` Juri Lelli
2018-10-18 9:48 ` Peter Zijlstra
2018-10-18 10:10 ` Juri Lelli
2018-10-18 10:38 ` luca abeni
2018-10-18 10:33 ` luca abeni
2018-10-19 13:14 ` Peter Zijlstra
2018-10-18 10:23 ` luca abeni
2018-10-18 10:47 ` Juri Lelli
2018-10-18 11:08 ` luca abeni
2018-10-18 12:21 ` Juri Lelli
2018-10-18 12:36 ` luca abeni
2018-10-19 11:39 ` Peter Zijlstra
2018-10-19 20:50 ` luca abeni
2018-10-24 12:03 ` Juri Lelli
2018-10-27 11:16 ` Dmitry Vyukov
2018-10-28 8:33 ` Juri Lelli
2018-10-30 10:45 ` Peter Zijlstra
2018-10-30 11:08 ` luca abeni
2018-10-31 16:18 ` Daniel Bristot de Oliveira
2018-10-31 16:40 ` Juri Lelli
2018-10-31 17:39 ` Peter Zijlstra
2018-10-31 17:58 ` Daniel Bristot de Oliveira
2018-11-01 5:55 ` Juri Lelli
2018-11-02 10:00 ` Daniel Bristot de Oliveira
2018-11-05 10:55 ` Juri Lelli
2018-11-07 10:12 ` Daniel Bristot de Oliveira
2018-10-31 17:38 ` Peter Zijlstra
2018-10-30 11:12 ` Juri Lelli
2018-11-06 11:44 ` Juri Lelli
2021-10-27 0:59 Hao Sun
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