linux-kernel - Re: [GIT PULL v2] sched: Make sleep inside atomic detection work on !PREEMPT

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Message-ID: <20110701125644.GD8508@somewhere>
Date:	Fri, 1 Jul 2011 14:56:46 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [GIT PULL v2] sched: Make sleep inside atomic detection work on
 !PREEMPT

On Fri, Jul 01, 2011 at 02:36:29PM +0200, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > On Fri, Jun 10, 2011 at 03:30:18PM +0200, Frederic Weisbecker wrote:
> > > Ingo,
> > > 
> > > Please pull the sched/core branch that can be found at:
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
> > > 	sched/core
> > 
> > Hi Ingo,
> > 
> > I have added Randy's ack on the last patch. To get it, please pull the v2 in
> > the following branch:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
> >        sched/core-v2
> > 
> > There are no other changes.
> 
> Hm, this triggers such warnings now:
> 
> Detected 2010.217 MHz processor.
> Marking TSC unstable due to TSCs unsynchronized
> Calibrating delay loop (skipped), value calculated using timer frequency.. 4022.95 BogoMIPS (lpj=6700723)
> pid_max: default: 4096 minimum: 301
> BUG: scheduling while atomic: swapper/0/0x10000002
> no locks held by swapper/0.
> Pid: 0, comm: swapper Not tainted 3.0.0-rc5-tip-01401-ga7adf5f-dirty #141020
> Call Trace:
>  [<ffffffff81ddb3b0>] __schedule_bug+0x60/0x65
>  [<ffffffff81dee803>] schedule+0x953/0x980
>  [<ffffffff81571e30>] ? serial8250_console_putchar+0x30/0x40
>  [<ffffffff81df177b>] ? _raw_spin_unlock+0x2b/0x50
>  [<ffffffff8107882a>] __cond_resched+0x2a/0x40
>  [<ffffffff81dee8e2>] _cond_resched+0x32/0x40
>  [<ffffffff81110ba8>] __alloc_pages_nodemask+0x1b8/0x880
>  [<ffffffff81df23ce>] ? common_interrupt+0xe/0x13
>  [<ffffffff81080649>] ? vprintk+0x359/0x530
>  [<ffffffff8113b4e7>] slob_new_pages+0x17/0x80
>  [<ffffffff8113bd13>] __kmalloc_node+0xa3/0x270
>  [<ffffffff81ddb6d5>] ? printk+0x41/0x43
>  [<ffffffff82738420>] pidmap_init+0x80/0xbf
>  [<ffffffff8272aa54>] start_kernel+0x28b/0x300
>  [<ffffffff8272a2ee>] x86_64_start_reservations+0xfe/0x102
>  [<ffffffff8272a3e2>] x86_64_start_kernel+0xf0/0xf7
> Security Framework initialized
> AppArmor: AppArmor initialized
> Mount-cache hash table entries: 256
> Initializing cgroup subsys cpuacct
> 
> Not sure we want to warn about schedule during early init, or can it 
> cause problems and should thus be fixed? I bet there's more such 
> instances.

I believe this is harmless because no other other tasks than init are queued at that
time. But I don't know, may be calling schedule() involves some things that
are not ready yet at that time.

Either we add a system_state check in schedule_debug() or we fix the callers
to not call schedule when system_state shows we are booting..
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