linux-kernel - Re: [PATCH -mm] oprofile: BUG: using smp_processor

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Date:	Mon, 22 Sep 2008 12:28:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrea Righi <righi.andrea@...il.com>
Cc:	robert.richter@....com, akpm@...ux-foundation.org,
	oprofile-list@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] oprofile: BUG: using smp_processor_id() in
	preemptible code


* Ingo Molnar <mingo@...e.hu> wrote:

> > +	local_irq_save(flags);
> >  	__get_cpu_var(switch_index) = 0;
> > +	local_irq_restore(flags);
> 
> either use __raw_get_cpu_var() if we are for sure not preemptible 
> here, or fix the preemption status of this codepath.

i've applied the patch below instead to tip/oprofile - agreed?

	Ingo

------------>
>From 45f197ade73ba95681b9803680c75352fc0a1c0a Mon Sep 17 00:00:00 2001
From: Andrea Righi <righi.andrea@...il.com>
Date: Sat, 20 Sep 2008 12:58:40 +0200
Subject: [PATCH] x86, oprofile: BUG: using smp_processor_id() in preemptible code

Add __raw access before setting per cpu variable switch_index, to avoid
the following BUG:

[  449.166827] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/6998
[  449.166848] caller is op_nmi_init+0xf0/0x2b0 [oprofile]
[  449.166855] Pid: 6998, comm: modprobe Not tainted 2.6.27-rc5-mm1 #29
[  449.166860] Call Trace:
[  449.166872]  [<ffffffff80362d67>] debug_smp_processor_id+0xd7/0xe0
[  449.166887]  [<ffffffffa00181c0>] op_nmi_init+0xf0/0x2b0 [oprofile]
[  449.166902]  [<ffffffffa0018000>] oprofile_init+0x0/0x60 [oprofile]
[  449.166915]  [<ffffffffa00180a9>] oprofile_arch_init+0x9/0x30 [oprofile]
[  449.166928]  [<ffffffffa001801e>] oprofile_init+0x1e/0x60 [oprofile]
[  449.166937]  [<ffffffff8020903b>] _stext+0x3b/0x160
[  449.166946]  [<ffffffff80477985>] __mutex_unlock_slowpath+0xe5/0x190
[  449.166955]  [<ffffffff80262c1a>] trace_hardirqs_on_caller+0xca/0x140
[  449.166965]  [<ffffffff8026f7fc>] sys_init_module+0xdc/0x210
[  449.166972]  [<ffffffff8020b7cb>] system_call_fastpath+0x16/0x1b

Signed-off-by: Andrea Righi <righi.andrea@...il.com>
Acked-by: Robert Richter <robert.richter@....com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/oprofile/nmi_int.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index fb4902b..4108d02 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -551,7 +551,7 @@ int __init op_nmi_init(struct oprofile_operations *ops)
 	}
 
 	/* default values, can be overwritten by model */
-	__get_cpu_var(switch_index) = 0;
+	__raw_get_cpu_var(switch_index) = 0;
 	ops->create_files = nmi_create_files;
 	ops->setup = nmi_setup;
 	ops->shutdown = nmi_shutdown;
--
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