[PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Robin Holt]

From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>

There are instances in the kernel where we would like to disable
CPU hotplug (from sysfs) during some important operation. Today
the freezer code depends on this and the code to do it was kinda
tailor-made for that.

Restructure the code and make it generic enough to be useful for
other usecases too.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Robin Holt <holt@sgi.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: the arch/x86 maintainers <x86@kernel.org>
Cc: Arm Mailing List <linux-arm-kernel@lists.infradead.org>
Cc: <stable@vger.kernel.org>

---

Changes since -v6:
 - Added a #define for non-hotplug case.
---
 include/linux/cpu.h |  3 +++
 kernel/cpu.c        | 27 +++++++++------------------
 2 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index c6f6e08..3e450c0 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -141,6 +141,8 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
 }
 #endif
 
+extern void cpu_hotplug_disable(void);
+extern void cpu_hotplug_enable(void);
 int cpu_up(unsigned int cpu);
 void notify_cpu_starting(unsigned int cpu);
 extern void cpu_maps_update_begin(void);
@@ -148,6 +150,7 @@ extern void cpu_maps_update_done(void);
 
 #else	/* CONFIG_SMP */
 
+#define cpu_hotplug_disable()	do { } while (0)
 #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
 
 static inline int register_cpu_notifier(struct notifier_block *nb)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index b5e4ab2..28769f5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -541,29 +541,20 @@ static int __init alloc_frozen_cpus(void)
 core_initcall(alloc_frozen_cpus);
 
 /*
- * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
- * hotplug when tasks are about to be frozen. Also, don't allow the freezer
- * to continue until any currently running CPU hotplug operation gets
- * completed.
- * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
- * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
- * CPU hotplug path and released only after it is complete. Thus, we
- * (and hence the freezer) will block here until any currently running CPU
- * hotplug operation gets completed.
+ * Wait for currently running CPU hotplug operations to complete (if any) and
+ * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
+ * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
+ * hotplug path before performing hotplug operations. So acquiring that lock
+ * guarantees mutual exclusion from any currently running hotplug operations.
  */
-void cpu_hotplug_disable_before_freeze(void)
+void cpu_hotplug_disable(void)
 {
 	cpu_maps_update_begin();
 	cpu_hotplug_disabled = 1;
 	cpu_maps_update_done();
 }
 
-
-/*
- * When tasks have been thawed, re-enable regular CPU hotplug (which had been
- * disabled while beginning to freeze tasks).
- */
-void cpu_hotplug_enable_after_thaw(void)
+void cpu_hotplug_enable(void)
 {
 	cpu_maps_update_begin();
 	cpu_hotplug_disabled = 0;
@@ -589,12 +580,12 @@ cpu_hotplug_pm_callback(struct notifier_block *nb,
 
 	case PM_SUSPEND_PREPARE:
 	case PM_HIBERNATION_PREPARE:
-		cpu_hotplug_disable_before_freeze();
+		cpu_hotplug_disable();
 		break;
 
 	case PM_POST_SUSPEND:
 	case PM_POST_HIBERNATION:
-		cpu_hotplug_enable_after_thaw();
+		cpu_hotplug_enable();
 		break;
 
 	default:
-- 
1.8.2.1

[PATCH -v8 02/11] Migrate shutdown/reboot to boot cpu.

[Robin Holt]

We recently noticed that reboot of a 1024 cpu machine takes approx 16
minutes of just stopping the cpus.  The slowdown was tracked to commit
f96972f.

The current implementation does all the work of hot removing the cpus
before halting the system.  We are switching to just migrating to the
boot cpu and then continuing with shutdown/reboot.

This also has the effect of not breaking x86's command line parameter for
specifying the reboot cpu.  Note, this code was shamelessly copied from
arch/x86/kernel/reboot.c with bits removed pertaining to the reboot_cpu
command line parameter.

Signed-off-by: Robin Holt <holt@sgi.com>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: the arch/x86 maintainers <x86@kernel.org>
Cc: Arm Mailing List <linux-arm-kernel@lists.infradead.org>
Cc: <stable@vger.kernel.org>

---

Changes since -v6:
 - Add #define for PF_THREAD_BOUND as compatibility to make stable easier.
 - Fixup s/reboot_cpu_id/reboot_cpu/
---
 kernel/sys.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index b95d3c7..14640d7 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -362,6 +362,29 @@ int unregister_reboot_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_reboot_notifier);
 
+/* Add backwards compatibility for stable trees. */
+#ifndef PF_NO_SETAFFINITY
+#define PF_NO_SETAFFINITY		PF_THREAD_BOUND
+#endif
+
+static void migrate_to_reboot_cpu(void)
+{
+	/* The boot cpu is always logical cpu 0 */
+	int reboot_cpu = 0;
+
+	cpu_hotplug_disable();
+
+	/* Make certain the cpu I'm about to reboot on is online */
+	if (!cpu_online(reboot_cpu))
+		reboot_cpu = cpumask_first(cpu_online_mask);
+
+	/* Prevent races with other tasks migrating this task */
+	current->flags |= PF_NO_SETAFFINITY;
+
+	/* Make certain I only run on the appropriate processor */
+	set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu));
+}
+
 /**
  *	kernel_restart - reboot the system
  *	@cmd: pointer to buffer containing command to execute for restart
@@ -373,7 +396,7 @@ EXPORT_SYMBOL(unregister_reboot_notifier);
 void kernel_restart(char *cmd)
 {
 	kernel_restart_prepare(cmd);
-	disable_nonboot_cpus();
+	migrate_to_reboot_cpu();
 	syscore_shutdown();
 	if (!cmd)
 		printk(KERN_EMERG "Restarting system.\n");
@@ -400,7 +423,7 @@ static void kernel_shutdown_prepare(enum system_states state)
 void kernel_halt(void)
 {
 	kernel_shutdown_prepare(SYSTEM_HALT);
-	disable_nonboot_cpus();
+	migrate_to_reboot_cpu();
 	syscore_shutdown();
 	printk(KERN_EMERG "System halted.\n");
 	kmsg_dump(KMSG_DUMP_HALT);
@@ -419,7 +442,7 @@ void kernel_power_off(void)
 	kernel_shutdown_prepare(SYSTEM_POWER_OFF);
 	if (pm_power_off_prepare)
 		pm_power_off_prepare();
-	disable_nonboot_cpus();
+	migrate_to_reboot_cpu();
 	syscore_shutdown();
 	printk(KERN_EMERG "Power down.\n");
 	kmsg_dump(KMSG_DUMP_POWEROFF);
-- 
1.8.2.1

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Andrew Morton]

On Tue,  7 May 2013 09:39:45 -0500 Robin Holt <holt@sgi.com> wrote:

> From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
> 
> There are instances in the kernel where we would like to disable
> CPU hotplug (from sysfs) during some important operation. Today
> the freezer code depends on this and the code to do it was kinda
> tailor-made for that.
> 
> Restructure the code and make it generic enough to be useful for
> other usecases too.
> 
> ...
>
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -141,6 +141,8 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
>  }
>  #endif
>  
> +extern void cpu_hotplug_disable(void);
> +extern void cpu_hotplug_enable(void);
>  int cpu_up(unsigned int cpu);
>  void notify_cpu_starting(unsigned int cpu);
>  extern void cpu_maps_update_begin(void);
> @@ -148,6 +150,7 @@ extern void cpu_maps_update_done(void);
>  
>  #else	/* CONFIG_SMP */
>  
> +#define cpu_hotplug_disable()	do { } while (0)
>  #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
>  

Breaks alpha allmodconfig because cpu_hotplug_disable() is absent from
vmlinux.

cpu_hotplug_disable() doesn't get compiled unless we've defined
CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
behind that!

I'll stick this in there and see what happens.

--- a/include/linux/cpu.h~cpu-hotplug-provide-a-generic-helper-to-disable-enable-cpu-hotplug-fix
+++ a/include/linux/cpu.h
@@ -141,8 +141,6 @@ static inline void unregister_cpu_notifi
 }
 #endif
 
-extern void cpu_hotplug_disable(void);
-extern void cpu_hotplug_enable(void);
 int cpu_up(unsigned int cpu);
 void notify_cpu_starting(unsigned int cpu);
 extern void cpu_maps_update_begin(void);
@@ -150,7 +148,6 @@ extern void cpu_maps_update_done(void);
 
 #else	/* CONFIG_SMP */
 
-#define cpu_hotplug_disable()	do { } while (0)
 #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
 
 static inline int register_cpu_notifier(struct notifier_block *nb)
@@ -171,6 +168,15 @@ static inline void cpu_maps_update_done(
 }
 
 #endif /* CONFIG_SMP */
+
+#ifdef CONFIG_PM_SLEEP_SMP
+extern void cpu_hotplug_enable(void);
+extern void cpu_hotplug_disable(void);
+#else
+#define cpu_hotplug_enable()	do { } while (0)
+#define cpu_hotplug_disable()	do { } while (0)
+#endif
+
 extern struct bus_type cpu_subsys;
 
 #ifdef CONFIG_HOTPLUG_CPU

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Rafael J. Wysocki]

On Thursday, May 09, 2013 03:01:21 PM Andrew Morton wrote:
> On Tue,  7 May 2013 09:39:45 -0500 Robin Holt <holt@sgi.com> wrote:
> 
> > From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
> > 
> > There are instances in the kernel where we would like to disable
> > CPU hotplug (from sysfs) during some important operation. Today
> > the freezer code depends on this and the code to do it was kinda
> > tailor-made for that.
> > 
> > Restructure the code and make it generic enough to be useful for
> > other usecases too.
> > 
> > ...
> >
> > --- a/include/linux/cpu.h
> > +++ b/include/linux/cpu.h
> > @@ -141,6 +141,8 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
> >  }
> >  #endif
> >  
> > +extern void cpu_hotplug_disable(void);
> > +extern void cpu_hotplug_enable(void);
> >  int cpu_up(unsigned int cpu);
> >  void notify_cpu_starting(unsigned int cpu);
> >  extern void cpu_maps_update_begin(void);
> > @@ -148,6 +150,7 @@ extern void cpu_maps_update_done(void);
> >  
> >  #else	/* CONFIG_SMP */
> >  
> > +#define cpu_hotplug_disable()	do { } while (0)
> >  #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
> >  
> 
> Breaks alpha allmodconfig because cpu_hotplug_disable() is absent from
> vmlinux.
> 
> cpu_hotplug_disable() doesn't get compiled unless we've defined
> CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
> behind that!

I suppose it was only used by suspend/hibernate code paths when this was
introduced.

Thanks,
Rafael

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Andrew Morton]

On Fri, 10 May 2013 13:11:51 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> ...
>
> > cpu_hotplug_disable() doesn't get compiled unless we've defined
> > CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
> > behind that!
> 
> I suppose it was only used by suspend/hibernate code paths when this was
> introduced.

OK, well I suspect that what I have now is simply wrong for Robin's
application.  Robin, can you please check this?  We probably want to
make the does-something version of cpu_hotplug_disable/enable available
if CONFIG_HOTPLUG_CPU.

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Robin Holt]

On Fri, May 10, 2013 at 10:03:24AM -0700, Andrew Morton wrote:
> On Fri, 10 May 2013 13:11:51 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> 
> > ...
> >
> > > cpu_hotplug_disable() doesn't get compiled unless we've defined
> > > CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
> > > behind that!
> > 
> > I suppose it was only used by suspend/hibernate code paths when this was
> > introduced.
> 
> OK, well I suspect that what I have now is simply wrong for Robin's
> application.  Robin, can you please check this?  We probably want to
> make the does-something version of cpu_hotplug_disable/enable available
> if CONFIG_HOTPLUG_CPU.

This patch came from "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
I think I need to defer.

I spent all day trying to get an alpha cross compiler to build an
unmodified kernel and modules, only to find I didn't need to go that
far and could reproduce the failure with just building vmlinux.

Sorry for my slow response,
Robin

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Srivatsa S. Bhat]

On 05/11/2013 09:46 AM, Robin Holt wrote:
> On Fri, May 10, 2013 at 10:03:24AM -0700, Andrew Morton wrote:
>> On Fri, 10 May 2013 13:11:51 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
>>
>>> ...
>>>
>>>> cpu_hotplug_disable() doesn't get compiled unless we've defined
>>>> CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
>>>> behind that!
>>>
>>> I suppose it was only used by suspend/hibernate code paths when this was
>>> introduced.
>>
>> OK, well I suspect that what I have now is simply wrong for Robin's
>> application.  Robin, can you please check this?  We probably want to
>> make the does-something version of cpu_hotplug_disable/enable available
>> if CONFIG_HOTPLUG_CPU.
> 
> This patch came from "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
> I think I need to defer.

Here is a revised patch, which should address all the problems, IMHO.
Let me know if you face any issues. (And thanks a lot for fixing up the
!SMP case in the previous version.)

--------------------------------------------------------------------->

From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Subject: [PATCH] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

There are instances in the kernel where we would like to disable
CPU hotplug (from sysfs) during some important operation. Today
the freezer code depends on this and the code to do it was kinda
tailor-made for that.

Restructure the code and make it generic enough to be useful for
other usecases too.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 include/linux/cpu.h |    4 ++++
 kernel/cpu.c        |   55 +++++++++++++++++++++------------------------------
 2 files changed, 27 insertions(+), 32 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index c6f6e08..9f3c7e8 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -175,6 +175,8 @@ extern struct bus_type cpu_subsys;
 
 extern void get_online_cpus(void);
 extern void put_online_cpus(void);
+extern void cpu_hotplug_disable(void);
+extern void cpu_hotplug_enable(void);
 #define hotcpu_notifier(fn, pri)	cpu_notifier(fn, pri)
 #define register_hotcpu_notifier(nb)	register_cpu_notifier(nb)
 #define unregister_hotcpu_notifier(nb)	unregister_cpu_notifier(nb)
@@ -198,6 +200,8 @@ static inline void cpu_hotplug_driver_unlock(void)
 
 #define get_online_cpus()	do { } while (0)
 #define put_online_cpus()	do { } while (0)
+#define cpu_hotplug_disable()	do { } while (0)
+#define cpu_hotplug_enable()	do { } while (0)
 #define hotcpu_notifier(fn, pri)	do { (void)(fn); } while (0)
 /* These aren't inline functions due to a GCC bug. */
 #define register_hotcpu_notifier(nb)	({ (void)(nb); 0; })
diff --git a/kernel/cpu.c b/kernel/cpu.c
index b5e4ab2..198a388 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -133,6 +133,27 @@ static void cpu_hotplug_done(void)
 	mutex_unlock(&cpu_hotplug.lock);
 }
 
+/*
+ * Wait for currently running CPU hotplug operations to complete (if any) and
+ * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
+ * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
+ * hotplug path before performing hotplug operations. So acquiring that lock
+ * guarantees mutual exclusion from any currently running hotplug operations.
+ */
+void cpu_hotplug_disable(void)
+{
+	cpu_maps_update_begin();
+	cpu_hotplug_disabled = 1;
+	cpu_maps_update_done();
+}
+
+void cpu_hotplug_enable(void)
+{
+	cpu_maps_update_begin();
+	cpu_hotplug_disabled = 0;
+	cpu_maps_update_done();
+}
+
 #else /* #if CONFIG_HOTPLUG_CPU */
 static void cpu_hotplug_begin(void) {}
 static void cpu_hotplug_done(void) {}
@@ -541,36 +562,6 @@ static int __init alloc_frozen_cpus(void)
 core_initcall(alloc_frozen_cpus);
 
 /*
- * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
- * hotplug when tasks are about to be frozen. Also, don't allow the freezer
- * to continue until any currently running CPU hotplug operation gets
- * completed.
- * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
- * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
- * CPU hotplug path and released only after it is complete. Thus, we
- * (and hence the freezer) will block here until any currently running CPU
- * hotplug operation gets completed.
- */
-void cpu_hotplug_disable_before_freeze(void)
-{
-	cpu_maps_update_begin();
-	cpu_hotplug_disabled = 1;
-	cpu_maps_update_done();
-}
-
-
-/*
- * When tasks have been thawed, re-enable regular CPU hotplug (which had been
- * disabled while beginning to freeze tasks).
- */
-void cpu_hotplug_enable_after_thaw(void)
-{
-	cpu_maps_update_begin();
-	cpu_hotplug_disabled = 0;
-	cpu_maps_update_done();
-}
-
-/*
  * When callbacks for CPU hotplug notifications are being executed, we must
  * ensure that the state of the system with respect to the tasks being frozen
  * or not, as reported by the notification, remains unchanged *throughout the
@@ -589,12 +580,12 @@ cpu_hotplug_pm_callback(struct notifier_block *nb,
 
 	case PM_SUSPEND_PREPARE:
 	case PM_HIBERNATION_PREPARE:
-		cpu_hotplug_disable_before_freeze();
+		cpu_hotplug_disable();
 		break;
 
 	case PM_POST_SUSPEND:
 	case PM_POST_HIBERNATION:
-		cpu_hotplug_enable_after_thaw();
+		cpu_hotplug_enable();
 		break;
 
 	default:

Re: [PATCH -v8 01/11] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug

[Robin Holt]

Thank you.  That fixed the alpha allmodconfig case for me.  I am currently
rebuilding all the arm defconfig files and will resubmit -v10 when that
is done.

Robin

On Sat, May 11, 2013 at 02:43:20PM +0530, Srivatsa S. Bhat wrote:
> On 05/11/2013 09:46 AM, Robin Holt wrote:
> > On Fri, May 10, 2013 at 10:03:24AM -0700, Andrew Morton wrote:
> >> On Fri, 10 May 2013 13:11:51 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> >>
> >>> ...
> >>>
> >>>> cpu_hotplug_disable() doesn't get compiled unless we've defined
> >>>> CONFIG_PM_SLEEP_SMP.  I cannot begin to imagine what the logic is
> >>>> behind that!
> >>>
> >>> I suppose it was only used by suspend/hibernate code paths when this was
> >>> introduced.
> >>
> >> OK, well I suspect that what I have now is simply wrong for Robin's
> >> application.  Robin, can you please check this?  We probably want to
> >> make the does-something version of cpu_hotplug_disable/enable available
> >> if CONFIG_HOTPLUG_CPU.
> > 
> > This patch came from "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
> > I think I need to defer.
> 
> Here is a revised patch, which should address all the problems, IMHO.
> Let me know if you face any issues. (And thanks a lot for fixing up the
> !SMP case in the previous version.)
> 
> --------------------------------------------------------------------->
> 
> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Subject: [PATCH] CPU hotplug: Provide a generic helper to disable/enable CPU hotplug
> 
> There are instances in the kernel where we would like to disable
> CPU hotplug (from sysfs) during some important operation. Today
> the freezer code depends on this and the code to do it was kinda
> tailor-made for that.
> 
> Restructure the code and make it generic enough to be useful for
> other usecases too.
> 
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---
> 
>  include/linux/cpu.h |    4 ++++
>  kernel/cpu.c        |   55 +++++++++++++++++++++------------------------------
>  2 files changed, 27 insertions(+), 32 deletions(-)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index c6f6e08..9f3c7e8 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -175,6 +175,8 @@ extern struct bus_type cpu_subsys;
>  
>  extern void get_online_cpus(void);
>  extern void put_online_cpus(void);
> +extern void cpu_hotplug_disable(void);
> +extern void cpu_hotplug_enable(void);
>  #define hotcpu_notifier(fn, pri)	cpu_notifier(fn, pri)
>  #define register_hotcpu_notifier(nb)	register_cpu_notifier(nb)
>  #define unregister_hotcpu_notifier(nb)	unregister_cpu_notifier(nb)
> @@ -198,6 +200,8 @@ static inline void cpu_hotplug_driver_unlock(void)
>  
>  #define get_online_cpus()	do { } while (0)
>  #define put_online_cpus()	do { } while (0)
> +#define cpu_hotplug_disable()	do { } while (0)
> +#define cpu_hotplug_enable()	do { } while (0)
>  #define hotcpu_notifier(fn, pri)	do { (void)(fn); } while (0)
>  /* These aren't inline functions due to a GCC bug. */
>  #define register_hotcpu_notifier(nb)	({ (void)(nb); 0; })
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index b5e4ab2..198a388 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -133,6 +133,27 @@ static void cpu_hotplug_done(void)
>  	mutex_unlock(&cpu_hotplug.lock);
>  }
>  
> +/*
> + * Wait for currently running CPU hotplug operations to complete (if any) and
> + * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
> + * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
> + * hotplug path before performing hotplug operations. So acquiring that lock
> + * guarantees mutual exclusion from any currently running hotplug operations.
> + */
> +void cpu_hotplug_disable(void)
> +{
> +	cpu_maps_update_begin();
> +	cpu_hotplug_disabled = 1;
> +	cpu_maps_update_done();
> +}
> +
> +void cpu_hotplug_enable(void)
> +{
> +	cpu_maps_update_begin();
> +	cpu_hotplug_disabled = 0;
> +	cpu_maps_update_done();
> +}
> +
>  #else /* #if CONFIG_HOTPLUG_CPU */
>  static void cpu_hotplug_begin(void) {}
>  static void cpu_hotplug_done(void) {}
> @@ -541,36 +562,6 @@ static int __init alloc_frozen_cpus(void)
>  core_initcall(alloc_frozen_cpus);
>  
>  /*
> - * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
> - * hotplug when tasks are about to be frozen. Also, don't allow the freezer
> - * to continue until any currently running CPU hotplug operation gets
> - * completed.
> - * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
> - * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
> - * CPU hotplug path and released only after it is complete. Thus, we
> - * (and hence the freezer) will block here until any currently running CPU
> - * hotplug operation gets completed.
> - */
> -void cpu_hotplug_disable_before_freeze(void)
> -{
> -	cpu_maps_update_begin();
> -	cpu_hotplug_disabled = 1;
> -	cpu_maps_update_done();
> -}
> -
> -
> -/*
> - * When tasks have been thawed, re-enable regular CPU hotplug (which had been
> - * disabled while beginning to freeze tasks).
> - */
> -void cpu_hotplug_enable_after_thaw(void)
> -{
> -	cpu_maps_update_begin();
> -	cpu_hotplug_disabled = 0;
> -	cpu_maps_update_done();
> -}
> -
> -/*
>   * When callbacks for CPU hotplug notifications are being executed, we must
>   * ensure that the state of the system with respect to the tasks being frozen
>   * or not, as reported by the notification, remains unchanged *throughout the
> @@ -589,12 +580,12 @@ cpu_hotplug_pm_callback(struct notifier_block *nb,
>  
>  	case PM_SUSPEND_PREPARE:
>  	case PM_HIBERNATION_PREPARE:
> -		cpu_hotplug_disable_before_freeze();
> +		cpu_hotplug_disable();
>  		break;
>  
>  	case PM_POST_SUSPEND:
>  	case PM_POST_HIBERNATION:
> -		cpu_hotplug_enable_after_thaw();
> +		cpu_hotplug_enable();
>  		break;
>  
>  	default:
>