linux-kernel - [PATCH 2/9] kernel/cpu.c: Add arch dependent cpu map update functions

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Date:	Fri,  4 Nov 2011 15:03:54 -0700
From:	"Fenghua Yu" <fenghua.yu@...el.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>,
	"H Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Tony Luck" <tony.luck@...el.com>,
	"Suresh B Siddha" <suresh.b.siddha@...el.com>,
	"Len Brown" <len.brown@...el.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH 2/9] kernel/cpu.c: Add arch dependent cpu map update functions

From: Fenghua Yu <fenghua.yu@...el.com>

Because resume from hibernate and suspend always starts from CPU0 on x86 BIOS,
we need to check if CPU0 is online before hibernate or suspend. This causes a
race condition on cpu_online_map.

To cope with the race condition, we add arch_cpu_maps_update_begin() and
arch_cpu_maps_update_done() during cpu_down() and cpu_up(). The functions are
empty on non x86 platforms and are overriden on x86 platforms with real
functions to deal with the race condition.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 kernel/cpu.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 12b7458..4d80365 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -20,6 +20,14 @@
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
 
+void __weak arch_cpu_maps_update_begin(void)
+{
+}
+
+void __weak arch_cpu_maps_update_done(void)
+{
+}
+
 /*
  * The following two API's must be used when attempting
  * to serialize the updates to cpu_online_mask, cpu_present_mask.
@@ -274,6 +282,7 @@ int __ref cpu_down(unsigned int cpu)
 	int err;
 
 	cpu_maps_update_begin();
+	arch_cpu_maps_update_begin();
 
 	if (cpu_hotplug_disabled) {
 		err = -EBUSY;
@@ -284,6 +293,7 @@ int __ref cpu_down(unsigned int cpu)
 
 out:
 	cpu_maps_update_done();
+	arch_cpu_maps_update_done();
 	return err;
 }
 EXPORT_SYMBOL(cpu_down);
@@ -367,6 +377,7 @@ int __cpuinit cpu_up(unsigned int cpu)
 #endif
 
 	cpu_maps_update_begin();
+	arch_cpu_maps_update_begin();
 
 	if (cpu_hotplug_disabled) {
 		err = -EBUSY;
@@ -377,6 +388,7 @@ int __cpuinit cpu_up(unsigned int cpu)
 
 out:
 	cpu_maps_update_done();
+	arch_cpu_maps_update_done();
 	return err;
 }
 
-- 
1.6.0.3

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