linux-kernel - Re: [PATCH] x86/oprofile: disable preemption in nmi

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Message-ID: <20080622074018.GA3163@damson.getinternet.no>
Date:	Sun, 22 Jun 2008 09:40:18 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Johannes Weiner <hannes@...urebad.de>
Cc:	Ingo Molnar <mingo@...e.hu>, Philippe Elie <phil.el@...adoo.fr>,
	oprofile-list@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/oprofile: disable preemption in nmi_shutdown

Hi,

On Sun, Jun 22, 2008 at 9:30 AM, Johannes Weiner <hannes@...urebad.de> wrote:
> Vegard Nossum <vegard.nossum@...il.com> writes:
>>  static void nmi_shutdown(void)
>>  {
>> -     struct op_msrs *msrs = &__get_cpu_var(cpu_msrs);
>> +     struct op_msrs *msrs;
>> +
>> +     preempt_disable();
>> +     msrs = &__get_cpu_var(cpu_msrs);
>>       nmi_enabled = 0;
>>       on_each_cpu(nmi_cpu_shutdown, NULL, 0, 1);
>>       unregister_die_notifier(&profile_exceptions_nb);
>>       model->shutdown(msrs);
>>       free_msrs();
>> +     preempt_enable();
>
> Have a look at get_cpu_var() and put_cpu_var(), that is exactly the
> pattern.

Thanks! How about this instead?


Vegard


From: Vegard Nossum <vegard.nossum@...il.com>
Date: Sat, 21 Jun 2008 23:44:19 +0200
Subject: [PATCH] x86/oprofile: disable preemption in nmi_shutdown

    BUG: using smp_processor_id() in preemptible [00000000] code: oprofiled/27301
    caller is nmi_shutdown+0x11/0x60
    Pid: 27301, comm: oprofiled Not tainted 2.6.26-rc7 #25
     [<c028a90d>] debug_smp_processor_id+0xbd/0xc0
     [<c045fba1>] nmi_shutdown+0x11/0x60
     [<c045dd4a>] oprofile_shutdown+0x2a/0x60

Note that we don't need this for the other functions, since they are all
called with on_each_cpu() (which disables preemption for us anyway).

Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
---
 arch/x86/oprofile/nmi_int.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index cc48d3f..2b6ad5b 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -269,12 +269,13 @@ static void nmi_cpu_shutdown(void *dummy)
 
 static void nmi_shutdown(void)
 {
-	struct op_msrs *msrs = &__get_cpu_var(cpu_msrs);
+	struct op_msrs *msrs = &get_cpu_var(cpu_msrs);
 	nmi_enabled = 0;
 	on_each_cpu(nmi_cpu_shutdown, NULL, 0, 1);
 	unregister_die_notifier(&profile_exceptions_nb);
 	model->shutdown(msrs);
 	free_msrs();
+	put_cpu_var(cpu_msrs);
 }
 
 static void nmi_cpu_start(void *dummy)
-- 
1.5.4.1

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