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

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Message-ID: <20080621215518.GA5715@damson.getinternet.no>
Date:	Sat, 21 Jun 2008 23:55:18 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Ingo Molnar <mingo@...e.hu>, Philippe Elie <phil.el@...adoo.fr>
Cc:	oprofile-list@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/oprofile: disable preemption in nmi_shutdown

Hi,

Does this look correct? I didn't really play with preemption before, but
as far as I can tell, this is the right thing to do.

I don't really get why model->shutdown(msrs) is done only for one of the
CPUs, but my patch assumes that this is correct. (If that had been done
from inside nmi_shutdown() for each CPU, we wouldn't have had to get the
cpu var, and not needed to disable preemption.)

Please comment :-)


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 |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index cc48d3f..4a177b4 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -269,12 +269,16 @@ 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;
+
+	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();
 }
 
 static void nmi_cpu_start(void *dummy)
-- 
1.5.4.1

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