[ 3.5.y.z extended stable ] Patch "reboot: rigrate shutdown/reboot to boot cpu" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    reboot: rigrate shutdown/reboot to boot cpu

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f36854cc4eb7bdb7e3e46beb6c3eed7c89e70302 Mon Sep 17 00:00:00 2001
From: Robin Holt <holt at sgi.com>
Date: Wed, 12 Jun 2013 14:04:37 -0700
Subject: [PATCH] reboot: rigrate shutdown/reboot to boot cpu

commit cf7df378aa4ff7da3a44769b7ff6e9eef1a9f3db upstream.

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
f96972f2dc63 ("kernel/sys.c: call disable_nonboot_cpus() in
kernel_restart()").

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 at sgi.com>
Tested-by: Shawn Guo <shawn.guo at linaro.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat at linux.vnet.ibm.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Ingo Molnar <mingo at elte.hu>
Cc: Russ Anderson <rja at sgi.com>
Cc: Robin Holt <holt at sgi.com>
Cc: Russell King <linux at arm.linux.org.uk>
Cc: Guan Xuetao <gxt at mprc.pku.edu.cn>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/sys.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 0836a7f..1451e54 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -356,6 +356,29 @@ 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 cpu = 0;
+
+	cpu_hotplug_disable();
+
+	/* Make certain the cpu I'm about to reboot on is online */
+	if (!cpu_online(cpu))
+		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(cpu));
+}
+
 /**
  *	kernel_restart - reboot the system
  *	@cmd: pointer to buffer containing command to execute for restart
@@ -367,7 +390,7 @@ 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");
@@ -394,7 +417,7 @@ 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);
@@ -413,7 +436,7 @@ 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);
--
1.8.1.2