x86/intel_rdt: Call intel_rdt_sched_in() with preemption disabled

intel_rdt_sched_in() must be called with preemption disabled because the
function accesses percpu variables (pqr_state and closid).

If a task moves itself via move_myself() preemption is enabled, which
violates the calling convention and can result in incorrect closid
selection when the task gets preempted or migrated.

Add the required protection and a comment about the calling convention.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Cc: "Ravi V Shankar" <ravi.v.shankar@intel.com>
Cc: "Tony Luck" <tony.luck@intel.com>
Cc: "Marcelo Tosatti" <mtosatti@redhat.com>
Cc: "Sai Prakhya" <sai.praneeth.prakhya@intel.com>
Cc: "Vikas Shivappa" <vikas.shivappa@linux.intel.com>
Cc: "H. Peter Anvin" <h.peter.anvin@intel.com>
Link: http://lkml.kernel.org/r/1480625714-54246-1-git-send-email-fenghua.yu@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/intel_rdt.h

@@ -192,6 +192,8 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
  *   resctrl file system.
  * - Caches the per cpu CLOSid values and does the MSR write only
  *   when a task with a different CLOSid is scheduled in.
+ *
+ * Must be called with preemption disabled.
  */
 static inline void intel_rdt_sched_in(void)
 {

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -326,8 +326,10 @@ static void move_myself(struct callback_head *head)
 		kfree(rdtgrp);
 	}
 
+	preempt_disable();
 	/* update PQR_ASSOC MSR to make resource group go into effect */
 	intel_rdt_sched_in();
+	preempt_enable();
 
 	kfree(callback);
 }