From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 14 Jun 2013 17:16:35 +0200
Subject: kernel/hotplug: restore original cpu mask oncpu/down
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 48dd3113452811adb62bbf47d7dd8d2e45367e39
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

If a task which is allowed to run only on CPU X puts CPU Y down then it
will be allowed on all CPUs but the on CPU Y after it comes back from
kernel. This patch ensures that we don't lose the initial setting unless
the CPU the task is running is going down.


Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/cpu.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1068,6 +1068,7 @@ static int __ref _cpu_down(unsigned int
 	int prev_state, ret = 0;
 	int mycpu;
 	cpumask_var_t cpumask;
+	cpumask_var_t cpumask_org;
 
 	if (num_online_cpus() == 1)
 		return -EBUSY;
@@ -1078,6 +1079,12 @@ static int __ref _cpu_down(unsigned int
 	/* Move the downtaker off the unplug cpu */
 	if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
 		return -ENOMEM;
+	if (!alloc_cpumask_var(&cpumask_org, GFP_KERNEL))  {
+		free_cpumask_var(cpumask);
+		return -ENOMEM;
+	}
+
+	cpumask_copy(cpumask_org, &current->cpus_mask);
 	cpumask_andnot(cpumask, cpu_online_mask, cpumask_of(cpu));
 	set_cpus_allowed_ptr(current, cpumask);
 	free_cpumask_var(cpumask);
@@ -1086,7 +1093,8 @@ static int __ref _cpu_down(unsigned int
 	if (mycpu == cpu) {
 		printk(KERN_ERR "Yuck! Still on unplug CPU\n!");
 		migrate_enable();
-		return -EBUSY;
+		ret = -EBUSY;
+		goto restore_cpus;
 	}
 
 	cpu_hotplug_begin();
@@ -1136,6 +1144,9 @@ static int __ref _cpu_down(unsigned int
 out_cancel:
 	cpu_hotplug_done();
 	migrate_enable();
+restore_cpus:
+	set_cpus_allowed_ptr(current, cpumask_org);
+	free_cpumask_var(cpumask_org);
 	return ret;
 }