Bug-fixes for regressions:

- xen/tmem stopped working after a certain combination of modprobe/swapon was used
  - cpu online/offlining would trigger WARN_ON.
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Merge tag 'stable/for-linus-3.10-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen

Pull xen fixes from Konrad Rzeszutek Wilk:
 "Two bug-fixes for regressions:
   - xen/tmem stopped working after a certain combination of
     modprobe/swapon was used
   - cpu online/offlining would trigger WARN_ON."

* tag 'stable/for-linus-3.10-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
  xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
  xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU.

arch/x86/xen/smp.c

@@ -17,6 +17,7 @@
 #include <linux/slab.h>
 #include <linux/smp.h>
 #include <linux/irq_work.h>
+#include <linux/tick.h>
 
 #include <asm/paravirt.h>
 #include <asm/desc.h>
@@ -447,6 +448,13 @@ static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */
 	play_dead_common();
 	HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
 	cpu_bringup();
+	/*
+	 * commit 4b0c0f294 (tick: Cleanup NOHZ per cpu data on cpu down)
+	 * clears certain data that the cpu_idle loop (which called us
+	 * and that we return from) expects. The only way to get that
+	 * data back is to call:
+	 */
+	tick_nohz_idle_enter();
 }
 
 #else /* !CONFIG_HOTPLUG_CPU */

drivers/xen/tmem.c

@@ -379,10 +379,10 @@ static int xen_tmem_init(void)
 #ifdef CONFIG_FRONTSWAP
 	if (tmem_enabled && frontswap) {
 		char *s = "";
-		struct frontswap_ops *old_ops =
-			frontswap_register_ops(&tmem_frontswap_ops);
+		struct frontswap_ops *old_ops;
 
 		tmem_frontswap_poolid = -1;
+		old_ops = frontswap_register_ops(&tmem_frontswap_ops);
 		if (IS_ERR(old_ops) || old_ops) {
 			if (IS_ERR(old_ops))
 				return PTR_ERR(old_ops);