Re: [PATCH -mm][resend] Disable CPU hotplug during suspend

Rafael J. Wysocki
2006-07-29T23:08:35Z

On Saturday 29 July 2006 23:40, Nathan Lynch wrote:
> Rafael J. Wysocki wrote:
> > On Saturday 29 July 2006 00:40, Nathan Lynch wrote:
> >
> > > But maybe I'm misunderstanding the motivation for using cpu 0 here. I
> > > had assumed it was because on i386 (and others?) the BSP can't be
> > > offlined. Is there some other reason?
> >
> > Yes.
> >
> > First, the arch-dependent suspend code assumes implicitly that it will be
> > running on the BSP, so some strange things may happen if it doesn't.
> >
> > Second, we have to make sure that this function will always leaves the
> > same CPU online. It's a bit difficult to explain, but I'll do my best.
> > Suppose that disable_nonboot_cpus() exits running on CPU1, assuming it's
> > possible. Then the system memory state saved in the suspend image will
> > reflect this situation. Now the resume code will almost certainly run on the
> > BSP (say it's CPU0), but when the system memory is restored from the suspend
> > image the kernel will think it's running on CPU1.
> >
> > In the last patch I send yesterday I made disable_nonboot_cpus() check if the
> > first present CPU, first_cpu(cpu_present_map), is online, try to bring it up
> > if not and migrate itself to it before the loop over all online CPUs is run.
> >
> > I think that's general enough.
>
> I see, thanks for the explanation.
>
> It doesn't look like SMP swsusp would work reliably on platforms where
> there's a possibility of the cpu maps in the resume and saved images
> not matching (e.g. ppc64 logical partitions, where cpu 0 could be
> removed before suspending). But I guess that's largely a theoretical
> concern at this time. ;)

I think so. :-)

Appended is the full patch with corrections resulting from our discussion
here.

Andrew, could you please replace disable-cpu-hotplug-during-suspend.patch
with this one?

---
The current suspend code has to be run on one CPU, so we use the CPU
hotplug to take the non-boot CPUs offline on SMP machines. However, we
should also make sure that these CPUs will not be enabled by someone else
after we have disabled them.

The functions disable_nonboot_cpus() and enable_nonboot_cpus() are moved to
kernel/cpu.c, because they now refer to some stuff in there that should
better be static. Also it's better if disable_nonboot_cpus() returns an
error instead of panicking if something goes wrong, and
enable_nonboot_cpus() has no reason to panic(), because the CPUs may have
been enabled by the userland before it tries to take them online.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
---
include/linux/cpu.h | 8 ++
include/linux/suspend.h | 8 --
kernel/cpu.c | 138 +++++++++++++++++++++++++++++++++++++++++-------
kernel/power/Makefile | 2
kernel/power/disk.c | 7 ++
kernel/power/main.c | 10 +--
kernel/power/smp.c | 62 ---------------------
kernel/power/user.c | 14 +++-
8 files changed, 145 insertions(+), 104 deletions(-)

Index: linux-2.6.18-rc2-mm1/include/linux/suspend.h
===================================================================
--- linux-2.6.18-rc2-mm1.orig/include/linux/suspend.h 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/include/linux/suspend.h 2006-07-28 21:03:25.000000000 +0200
@@ -57,14 +57,6 @@ static inline int software_suspend(void)
}
#endif /* CONFIG_PM */

-#ifdef CONFIG_SUSPEND_SMP
-extern void disable_nonboot_cpus(void);
-extern void enable_nonboot_cpus(void);
-#else
-static inline void disable_nonboot_cpus(void) {}
-static inline void enable_nonboot_cpus(void) {}
-#endif
-
void save_processor_state(void);
void restore_processor_state(void);
struct saved_context;
Index: linux-2.6.18-rc2-mm1/kernel/power/smp.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/power/smp.c 2006-07-28 21:03:21.000000000 +0200
+++ /dev/null 1970-01-01 00:00:00.000000000 +0000
@@ -1,62 +0,0 @@
-/*
- * drivers/power/smp.c - Functions for stopping other CPUs.
- *
- * Copyright 2004 Pavel Machek <pavel@suse.cz>
- * Copyright (C) 2002-2003 Nigel Cunningham <ncunningham@clear.net.nz>
- *
- * This file is released under the GPLv2.
- */
-
-#undef DEBUG
-
-#include <linux/smp_lock.h>
-#include <linux/interrupt.h>
-#include <linux/suspend.h>
-#include <linux/module.h>
-#include <linux/cpu.h>
-#include <asm/atomic.h>
-#include <asm/tlbflush.h>
-
-/* This is protected by pm_sem semaphore */
-static cpumask_t frozen_cpus;
-
-void disable_nonboot_cpus(void)
-{
- int cpu, error;
-
- error = 0;
- cpus_clear(frozen_cpus);
- printk("Freezing cpus ...\n");
- for_each_online_cpu(cpu) {
- if (cpu == 0)
- continue;
- error = cpu_down(cpu);
- if (!error) {
- cpu_set(cpu, frozen_cpus);
- printk("CPU%d is down\n", cpu);
- continue;
- }
- printk("Error taking cpu %d down: %d\n", cpu, error);
- }
- BUG_ON(raw_smp_processor_id() != 0);
- if (error)
- panic("cpus not sleeping");
-}
-
-void enable_nonboot_cpus(void)
-{
- int cpu, error;
-
- printk("Thawing cpus ...\n");
- for_each_cpu_mask(cpu, frozen_cpus) {
- error = cpu_up(cpu);
- if (!error) {
- printk("CPU%d is up\n", cpu);
- continue;
- }
- printk("Error taking cpu %d up: %d\n", cpu, error);
- panic("Not enough cpus");
- }
- cpus_clear(frozen_cpus);
-}
-
Index: linux-2.6.18-rc2-mm1/kernel/power/disk.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/power/disk.c 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/power/disk.c 2006-07-28 23:25:13.000000000 +0200
@@ -18,6 +18,7 @@
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pm.h>
+#include <linux/cpu.h>

#include "power.h"

@@ -72,7 +73,10 @@ static int prepare_processes(void)
int error;

pm_prepare_console();
- disable_nonboot_cpus();
+
+ error = disable_nonboot_cpus();
+ if (error)
+ goto enable_cpus;

if (freeze_processes()) {
error = -EBUSY;
@@ -84,6 +88,7 @@ static int prepare_processes(void)
return 0;
thaw:
thaw_processes();
+enable_cpus:
enable_nonboot_cpus();
pm_restore_console();
return error;
Index: linux-2.6.18-rc2-mm1/kernel/power/main.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/power/main.c 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/power/main.c 2006-07-28 21:03:25.000000000 +0200
@@ -16,6 +16,7 @@
#include <linux/init.h>
#include <linux/pm.h>
#include <linux/console.h>
+#include <linux/cpu.h>

#include "power.h"

@@ -51,7 +52,7 @@ void pm_set_ops(struct pm_ops * ops)

static int suspend_prepare(suspend_state_t state)
{
- int error = 0;
+ int error;
unsigned int free_pages;

if (!pm_ops || !pm_ops->enter)
@@ -63,12 +64,9 @@ static int suspend_prepare(suspend_state

pm_prepare_console();

- disable_nonboot_cpus();
-
- if (num_online_cpus() != 1) {
- error = -EPERM;
+ error = disable_nonboot_cpus();
+ if (error)
goto Enable_cpu;
- }

if (freeze_processes()) {
error = -EAGAIN;
Index: linux-2.6.18-rc2-mm1/kernel/power/user.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/power/user.c 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/power/user.c 2006-07-28 21:03:25.000000000 +0200
@@ -19,6 +19,7 @@
#include <linux/swapops.h>
#include <linux/pm.h>
#include <linux/fs.h>
+#include <linux/cpu.h>

#include <asm/uaccess.h>

@@ -139,12 +140,15 @@ static int snapshot_ioctl(struct inode *
if (data->frozen)
break;
down(&pm_sem);
- disable_nonboot_cpus();
- if (freeze_processes()) {
- thaw_processes();
- enable_nonboot_cpus();
- error = -EBUSY;
+ error = disable_nonboot_cpus();
+ if (!error) {
+ error = freeze_processes();
+ if (error) {
+ thaw_processes();
+ error = -EBUSY;
+ }
}
+ enable_nonboot_cpus();
up(&pm_sem);
if (!error)
data->frozen = 1;
Index: linux-2.6.18-rc2-mm1/include/linux/cpu.h
===================================================================
--- linux-2.6.18-rc2-mm1.orig/include/linux/cpu.h 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/include/linux/cpu.h 2006-07-28 21:03:25.000000000 +0200
@@ -89,4 +89,12 @@ int cpu_down(unsigned int cpu);
static inline int cpu_is_offline(int cpu) { return 0; }
#endif

+#ifdef CONFIG_SUSPEND_SMP
+extern int disable_nonboot_cpus(void);
+extern void enable_nonboot_cpus(void);
+#else
+static inline int disable_nonboot_cpus(void) { return 0; }
+static inline void enable_nonboot_cpus(void) {}
+#endif
+
#endif /* _LINUX_CPU_H_ */
Index: linux-2.6.18-rc2-mm1/kernel/cpu.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/cpu.c 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/cpu.c 2006-07-28 23:25:08.000000000 +0200
@@ -21,6 +21,11 @@ static DEFINE_MUTEX(cpu_bitmask_lock);

static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);

+/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
+ * Should always be manipulated under cpu_add_remove_lock
+ */
+static int cpu_hotplug_disabled;
+
#ifdef CONFIG_HOTPLUG_CPU

/* Crappy recursive lock-takers in cpufreq! Complain loudly about idiots */
@@ -108,30 +113,25 @@ static int take_cpu_down(void *unused)
return 0;
}

-int cpu_down(unsigned int cpu)
+/* Requires cpu_add_remove_lock to be held */
+static int _cpu_down(unsigned int cpu)
{
int err;
struct task_struct *p;
cpumask_t old_allowed, tmp;

- mutex_lock(&cpu_add_remove_lock);
- if (num_online_cpus() == 1) {
- err = -EBUSY;
- goto out;
- }
+ if (num_online_cpus() == 1)
+ return -EBUSY;

- if (!cpu_online(cpu)) {
- err = -EINVAL;
- goto out;
- }
+ if (!cpu_online(cpu))
+ return -EINVAL;

err = blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
(void *)(long)cpu);
if (err == NOTIFY_BAD) {
printk("%s: attempt to take down CPU %u failed\n",
__FUNCTION__, cpu);
- err = -EINVAL;
- goto out;
+ return -EINVAL;
}

/* Ensure that we are not runnable on dying cpu */
@@ -179,22 +179,32 @@ out_thread:
err = kthread_stop(p);
out_allowed:
set_cpus_allowed(current, old_allowed);
-out:
+ return err;
+}
+
+int cpu_down(unsigned int cpu)
+{
+ int err = 0;
+
+ mutex_lock(&cpu_add_remove_lock);
+ if (cpu_hotplug_disabled)
+ err = -EBUSY;
+ else
+ err = _cpu_down(cpu);
+
mutex_unlock(&cpu_add_remove_lock);
return err;
}
#endif /*CONFIG_HOTPLUG_CPU*/

-int __devinit cpu_up(unsigned int cpu)
+/* Requires cpu_add_remove_lock to be held */
+static int __devinit _cpu_up(unsigned int cpu)
{
int ret;
void *hcpu = (void *)(long)cpu;

- mutex_lock(&cpu_add_remove_lock);
- if (cpu_online(cpu) || !cpu_present(cpu)) {
- ret = -EINVAL;
- goto out;
- }
+ if (cpu_online(cpu) || !cpu_present(cpu))
+ return -EINVAL;

ret = blocking_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
if (ret == NOTIFY_BAD) {
@@ -219,7 +229,95 @@ out_notify:
if (ret != 0)
blocking_notifier_call_chain(&cpu_chain,
CPU_UP_CANCELED, hcpu);
+
+ return ret;
+}
+
+int __devinit cpu_up(unsigned int cpu)
+{
+ int err = 0;
+
+ mutex_lock(&cpu_add_remove_lock);
+ if (cpu_hotplug_disabled)
+ err = -EBUSY;
+ else
+ err = _cpu_up(cpu);
+
+ mutex_unlock(&cpu_add_remove_lock);
+ return err;
+}
+
+#ifdef CONFIG_SUSPEND_SMP
+static cpumask_t frozen_cpus;
+
+int disable_nonboot_cpus(void)
+{
+ int cpu, first_cpu, error;
+
+ mutex_lock(&cpu_add_remove_lock);
+ first_cpu = first_cpu(cpu_present_map);
+ if (!cpu_online(first_cpu)) {
+ error = _cpu_up(first_cpu);
+ if (error) {
+ printk(KERN_ERR "Could not bring CPU%d up.\n",
+ first_cpu);
+ goto out;
+ }
+ }
+ error = set_cpus_allowed(current, cpumask_of_cpu(first_cpu));
+ if (error) {
+ printk(KERN_ERR "Could not run on CPU%d\n", first_cpu);
+ goto out;
+ }
+ /* We take down all of the non-boot CPUs in one shot to avoid races
+ * with the userspace trying to use the CPU hotplug at the same time
+ */
+ cpus_clear(frozen_cpus);
+ printk("Disabling non-boot CPUs ...\n");
+ for_each_online_cpu(cpu) {
+ if (cpu == first_cpu)
+ continue;
+ error = _cpu_down(cpu);
+ if (!error) {
+ cpu_set(cpu, frozen_cpus);
+ printk("CPU%d is down\n", cpu);
+ } else {
+ printk(KERN_ERR "Error taking CPU%d down: %d\n",
+ cpu, error);
+ break;
+ }
+ }
+ if (!error) {
+ BUG_ON(num_online_cpus() > 1);
+ /* Make sure the CPUs won't be enabled by someone else */
+ cpu_hotplug_disabled = 1;
+ } else {
+ printk(KERN_ERR "Non-boot CPUs are not disabled");
+ }
out:
mutex_unlock(&cpu_add_remove_lock);
- return ret;
+ return error;
+}
+
+void enable_nonboot_cpus(void)
+{
+ int cpu, error;
+
+ /* Allow everyone to use the CPU hotplug again */
+ mutex_lock(&cpu_add_remove_lock);
+ cpu_hotplug_disabled = 0;
+ mutex_unlock(&cpu_add_remove_lock);
+
+ printk("Enabling non-boot CPUs ...\n");
+ for_each_cpu_mask(cpu, frozen_cpus) {
+ error = cpu_up(cpu);
+ if (!error) {
+ printk("CPU%d is up\n", cpu);
+ continue;
+ }
+ printk(KERN_WARNING "Error taking CPU%d up: %d\n",
+ cpu, error);
+ }
+ cpus_clear(frozen_cpus);
}
+#endif
Index: linux-2.6.18-rc2-mm1/kernel/power/Makefile
===================================================================
--- linux-2.6.18-rc2-mm1.orig/kernel/power/Makefile 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/power/Makefile 2006-07-28 21:03:25.000000000 +0200
@@ -7,6 +7,4 @@ obj-y := main.o process.o console.o
obj-$(CONFIG_PM_LEGACY) += pm.o
obj-$(CONFIG_SOFTWARE_SUSPEND) += swsusp.o disk.o snapshot.o swap.o user.o

-obj-$(CONFIG_SUSPEND_SMP) += smp.o
-
obj-$(CONFIG_MAGIC_SYSRQ) += poweroff.o