linux-kernel - Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses)

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Date:	Wed, 4 Jun 2008 09:00:36 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Max Krasnyansky <maxk@...lcomm.com>, Paul Jackson <pj@....com>,
	Con Kolivas <kernel@...ivas.org>,
	"Derek L. Fults" <dfults@....com>, devik <devik@....cz>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Emmanuel Pacaud <emmanuel.pacaud@...v-poitiers.fr>,
	Frederik Deweerdt <deweerdt@...e.fr>,
	Ingo Molnar <mingo@...e.hu>,
	Matthew Dobson <colpatch@...ibm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>, rostedt@...dmis.org,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Randy.Dunlap" <rddunlap@...l.org>, suresh.b.siddha@...el.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses)

On Tue, Jun 03, 2008 at 09:40:10AM -0500, Dimitri Sivanich wrote:
> I tried the following scenario on an ia64 Altix running 2.6.26-rc4 with cpusets compiled in but cpuset fs unmounted.  Do your patches already address this?
> 
> $ taskset -cp 3 $$   (attach to cpu 3)
> pid 4591's current affinity list: 0-3
> pid 4591's new affinity list: 3
> $ echo 0 > /sys/devices/system/cpu/cpu2/online  (down cpu 2)
>   (above command hangs)
> 
> Backtrace of pid 4591 (bash)
> 
> Call Trace:
>  [<a00000010078e990>] schedule+0x1210/0x13c0
>                                 sp=e0000060b6dffc90 bsp=e0000060b6df11e0
>  [<a00000010078ef60>] schedule_timeout+0x40/0x180
>                                 sp=e0000060b6dffce0 bsp=e0000060b6df11b0
>  [<a00000010078d3e0>] wait_for_common+0x240/0x3c0
>                                 sp=e0000060b6dffd10 bsp=e0000060b6df1180
>  [<a00000010078d760>] wait_for_completion+0x40/0x60
>                                 sp=e0000060b6dffd40 bsp=e0000060b6df1160
>  [<a000000100114ee0>] __stop_machine_run+0x120/0x160
>                                 sp=e0000060b6dffd40 bsp=e0000060b6df1120
>  [<a000000100765ae0>] _cpu_down+0x2a0/0x600
>                                 sp=e0000060b6dffd80 bsp=e0000060b6df10c8
>  [<a000000100765ea0>] cpu_down+0x60/0xa0
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df10a0
>  [<a000000100768090>] store_online+0x50/0xe0
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df1070
>  [<a0000001004f8800>] sysdev_store+0x60/0xa0
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df1038
>  [<a00000010022e370>] sysfs_write_file+0x250/0x300
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df0fe0
>  [<a00000010018a750>] vfs_write+0x1b0/0x300
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df0f90
>  [<a00000010018b350>] sys_write+0x70/0xe0
>                                 sp=e0000060b6dffe20 bsp=e0000060b6df0f18
>  [<a00000010000af80>] ia64_ret_from_syscall+0x0/0x20
>                                 sp=e0000060b6dffe30 bsp=e0000060b6df0f18
>  [<a000000000010720>] ia64_ivt+0xffffffff00010720/0x400
>                                 sp=e0000060b6e00000 bsp=e0000060b6df0f18

The following workaround alleviates the symptom and hopefully is a hint as to the solution:
	echo -1 > /proc/sys/kernel/sched_rt_runtime_us
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