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From: Thomas Gleixner <tglx@linutronix.de>
To: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Ingo Molnar <mingo@kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
	Tejun Heo <tj@kernel.org>, David Rientjes <rientjes@google.com>,
	venki@google.com
Subject: Re: [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1
Date: Thu, 3 May 2012 11:41:45 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1205031137270.6271@ionos> (raw)
In-Reply-To: <1334966930.28674.245.camel@sbsiddha-desk.sc.intel.com>

On Fri, 20 Apr 2012, Suresh Siddha wrote:
> On Fri, 2012-04-20 at 15:47 +0200, Thomas Gleixner wrote:
> > On Fri, 20 Apr 2012, Peter Zijlstra wrote:
> > 
> > > On Fri, 2012-04-20 at 13:05 +0000, Thomas Gleixner wrote:
> > > > This first part moves the idle thread management for non-boot cpus
> > > > into the core. fork_idle() is called in a workqueue as it is
> > > > implemented in a few architectures already. This is necessary when not
> > > > all cpus are brought up by the early boot code as otherwise we would
> > > > take a ref on the user task VM of the thread which brings the cpu up
> > > > via the sysfs interface. 
> > > 
> > > So I was thinking about this and I think we should make that kthreadd
> > > instead of a random workqueue thread due to all that cgroup crap. People
> > > are wanting to place all sorts of kernel threads in cgroups and I'm
> > > still arguing that kthreadd should not be allowed in cgroups.
> > 
> > So your fear is that the idle_thread will end up in some random cgroup
> > because some illdesigned user space code decided to stick kernel
> > threads into cgroups.
> > 
> > Can we please have some sanity restrictions on this cgroup muck? I
> > don't care when user space creates cgroups in circles, but holding the
> > whole kernel hostage of this madness is going too far.
> > 
> 
> Also, do we really need the workqueue/kthreadd based allocation? Just
> like the percpu areas getting allocated for each possible cpu during
> boot, shouldn't we extend this to the per-cpu idle threads too? So
> something like the appended should be ok to?

The idea is correct, there are just a few problems :)
 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> ---
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 05c46ba..a5144ab 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -303,10 +303,6 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
>  
>  	cpu_hotplug_begin();
>  
> -	ret = smpboot_prepare(cpu);
> -	if (ret)
> -		goto out;
> -

If we failed to allocate an idle_thread for this cpu in smp_init()
then we unconditionally call __cpu_up() with a NULL pointer. That
might surprise the arch code :)

Aside of that, we now miss to reinitialize the idle thread. We call
init_idle() once when we allocate the thread, but not after a cpu
offline operation. That might leave stuff in weird state.

Thanks,

	tglx

  reply	other threads:[~2012-05-03  9:42 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-20 13:05 Thomas Gleixner
2012-04-20 13:05 ` [patch 01/18] m32r: Remove pointless function prototypes Thomas Gleixner
2012-04-28  9:01   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 02/18] smp: Add task_struct argument to __cpu_up() Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-23  7:58   ` Jesper Nilsson
2012-04-23  7:58     ` Jesper Nilsson
2012-04-28  9:02   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 03/18] smp: Add generic smpboot facility Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-20 20:07   ` Yinghai Lu
2012-04-20 20:07     ` Yinghai Lu
2012-04-21  2:07   ` Stephen Rothwell
2012-04-21  2:07     ` Stephen Rothwell
2012-04-28  9:04   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 04/18] smp: Provide generic idle thread allocation Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-20 16:21   ` Sam Ravnborg
2012-04-20 16:21     ` Sam Ravnborg
2012-04-20 18:55     ` Thomas Gleixner
2012-04-20 18:55       ` Thomas Gleixner
2012-04-21  2:20   ` Stephen Rothwell
2012-04-21  2:20     ` Stephen Rothwell
2012-04-21  2:25   ` Frank Rowand
2012-04-21  2:25     ` Frank Rowand
2012-04-28  9:05   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 05/18] x86: Add task_struct argument to smp_ops.cpu_up Thomas Gleixner
2012-04-28  9:05   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 06/18] x86: Use generic idle thread allocation Thomas Gleixner
2012-04-28  9:06   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 07/18] powerpc: " Thomas Gleixner
2012-04-28  9:07   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-28 22:51     ` Benjamin Herrenschmidt
2012-04-20 13:05 ` [patch 08/18] ia64: " Thomas Gleixner
2012-04-28  9:08   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 09/18] arm: " Thomas Gleixner
2012-04-28  9:09   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 11/18] hexagon: " Thomas Gleixner
2012-04-24 16:47   ` Richard Kuo
2012-04-28  9:10   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 10/18] mips: " Thomas Gleixner
2012-04-28  9:10   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 12/18] s390: " Thomas Gleixner
2012-04-23  7:09   ` Martin Schwidefsky
2012-04-28  9:11   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 13/18] blackfin: " Thomas Gleixner
2012-04-28  9:13   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 14/18] cris: " Thomas Gleixner
2012-04-23  7:57   ` Jesper Nilsson
2012-04-28  9:12   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 15/18] sh: " Thomas Gleixner
2012-04-21  3:18   ` Paul Mundt
2012-04-28  9:14   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 16/18] alpha: " Thomas Gleixner
2012-04-28  9:15   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 17/18] parisc: " Thomas Gleixner
2012-04-28  9:16   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 18/18] sparc: " Thomas Gleixner
2012-04-22 19:52   ` David Miller
2012-04-28  9:15   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:16 ` [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 Thomas Gleixner
2012-04-20 13:21 ` Peter Zijlstra
2012-04-20 13:47   ` Thomas Gleixner
2012-04-21  0:08     ` Suresh Siddha
2012-05-03  9:41       ` Thomas Gleixner [this message]
2012-05-03 23:42         ` Suresh Siddha
2012-05-03 17:43       ` [tip:smp/hotplug] smp, idle: Allocate idle thread for each possible cpu during boot tip-bot for Suresh Siddha
2012-04-20 15:42   ` [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 Tejun Heo
2012-04-20 15:49     ` Peter Zijlstra
2012-04-20 15:56       ` Thomas Gleixner
2012-04-20 13:56 ` Srivatsa S. Bhat
2012-04-20 14:18   ` Thomas Gleixner
2012-04-24 18:44     ` Konrad Rzeszutek Wilk
2012-05-21  1:42     ` Rusty Russell
2012-05-21  8:25       ` Thomas Gleixner
2012-05-22  0:53         ` Rusty Russell
2012-04-20 14:06 ` richard -rw- weinberger
2012-04-20 14:19   ` Thomas Gleixner
2012-04-20 14:27 ` James Bottomley
2012-04-20 17:55 ` Paul E. McKenney
2012-04-20 23:11 ` Venki Pallipadi
2012-04-21  1:04 ` Frank Rowand
2012-04-21  1:55   ` Frank Rowand
2012-04-22 21:01 ` Chris Metcalf
2012-04-22 21:01   ` Chris Metcalf
2012-04-22 21:01   ` Chris Metcalf
2012-04-30  8:05 ` Santosh Shilimkar

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