linux-kernel - [PATCH v2 30/45] x86/xen: Use get/put_online_cpus

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Message-ID: <20130625203057.16593.50205.stgit@srivatsabhat.in.ibm.com>
Date:	Wed, 26 Jun 2013 02:00:57 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org, laijs@...fujitsu.com
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, sbw@....edu, fweisbec@...il.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	srivatsa.bhat@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v2 30/45] x86/xen: Use get/put_online_cpus_atomic() to prevent
 CPU offline

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: xen-devel@...ts.xensource.com
Cc: virtualization@...ts.linux-foundation.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 arch/x86/xen/mmu.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index fdc3ba2..3229c4f 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -39,6 +39,7 @@
  * Jeremy Fitzhardinge <jeremy@...source.com>, XenSource Inc, 2007
  */
 #include <linux/sched.h>
+#include <linux/cpu.h>
 #include <linux/highmem.h>
 #include <linux/debugfs.h>
 #include <linux/bug.h>
@@ -1163,9 +1164,13 @@ static void xen_drop_mm_ref(struct mm_struct *mm)
  */
 static void xen_exit_mmap(struct mm_struct *mm)
 {
-	get_cpu();		/* make sure we don't move around */
+	/*
+	 * Make sure we don't move around, and also prevent CPUs from
+	 * going offline.
+	 */
+	get_online_cpus_atomic();
 	xen_drop_mm_ref(mm);
-	put_cpu();
+	put_online_cpus_atomic();
 
 	spin_lock(&mm->page_table_lock);
 

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