linux-kernel - Re: [patch 1/2] stop_machine: enable __stop_machine() to be called from the cpu online path

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Date:	Tue, 7 Jun 2011 20:02:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	tglx@...utronix.de, hpa@...or.com, trenn@...ell.com,
	prarit@...hat.com, tj@...nel.org, linux-kernel@...r.kernel.org,
	youquan.song@...el.com, stable@...nel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch 1/2] stop_machine: enable __stop_machine() to be called
 from the cpu online path


* Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> Currently stop machine infrastructure can be called only from a cpu 
> that is online. But for !CONFIG_SMP, we do allow calling 
> __stop_machine() before the cpu is online.
> 
> x86 for example requires stop machine infrastructure in the cpu 
> online path and currently implements its own stop machine (using 
> stop_one_cpu_nowait()) for MTRR initialization in the cpu online 
> path.
> 
> Enhance the __stop_machine() so that it can be called before the 
> cpu is onlined. This will pave the way for code consolidation and 
> address potential deadlocks caused by multiple mechanisms of doing 
> system wide rendezvous.
> 
> This will also address the behavioral differences of 
> __stop_machine() between SMP and UP builds.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Cc: stable@...nel.org    # v2.6.35+
> ---
>  kernel/stop_machine.c |   62 +++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 57 insertions(+), 5 deletions(-)

This patch is causing problems:

 [   19.835435] BUG: using smp_processor_id() in preemptible [00000000] code: perf/701
 [   19.838718] caller is __stop_machine+0x3c/0xbe
 [   19.842079] Pid: 701, comm: perf Not tainted 3.0.0-rc2-tip+ #132432
 [   19.845378] Call Trace:
 [   19.847838]  [<c1112431>] ? debug_smp_processor_id+0xbd/0xd0
 [   19.848712]  [<c1050be6>] ? __stop_machine+0x3c/0xbe
 [   19.852046]  [<c1005b74>] ? text_poke+0xec/0xec
 [   19.855379]  [<c1014447>] ? do_page_fault+0xb0/0x361
 [   19.858711]  [<c1005f00>] ? text_poke_smp+0x48/0x4f
 [   19.862044]  [<c1014447>] ? do_page_fault+0xb0/0x361
 [   19.865378]  [<c100519c>] ? arch_jump_label_transform+0x50/0x64
 [   19.868712]  [<c103d61a>] ? __jump_label_update+0x28/0x39
 [   19.872044]  [<c103d647>] ? jump_label_update+0x1c/0x49
 [   19.875377]  [<c103d892>] ? jump_label_inc+0x38/0x40
 [   19.878710]  [<c105cfaf>] ? perf_swevent_init+0x118/0x129
 [   19.882044]  [<c10625b6>] ? perf_init_event+0x47/0x7c
 [   19.885376]  [<c10627f7>] ? perf_event_alloc+0x20c/0x416
 [   19.888710]  [<c1062fb1>] ? sys_perf_event_open+0x313/0x634
 [   19.892042]  [<c101469a>] ? do_page_fault+0x303/0x361
 [   19.895379]  [<c1281e70>] ? sysenter_do_call+0x12/0x26

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