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
next prev parent reply other threads:[~2012-05-03 9:42 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-20 13:05 [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 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
2012-04-23 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 20:07 ` Yinghai Lu
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 16:21 ` Sam Ravnborg
2012-04-20 18:55 ` Thomas Gleixner
2012-04-21 2:20 ` Stephen Rothwell
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
2012-04-30 8:05 ` Santosh Shilimkar
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