x86/intel_rdt: Update task closid immediately on CPU in rmdir and unmount

When removing a sub directory/rdtgroup by rmdir or umount, closid in a
task in the sub directory is set to default rdtgroup's closid which is 0.
If the task is running on a CPU, the PQR_ASSOC MSR is only updated
when the task runs through a context switch. Up to the context switch,
the task runs with the wrong closid.

Make the change immediately effective by invoking a smp function call on
all CPUs which are running moved task. If one of the affected tasks was
moved or scheduled out before the function call is executed on the CPU the
only damage is the extra interruption of the CPU.

[ tglx: Reworked it to avoid blindly interrupting all CPUs and extra loops ]

Signed-off-by: Fenghua Yu <[email protected]>
Cc: "Ravi V Shankar" <[email protected]>
Cc: "Tony Luck" <[email protected]>
Cc: "Sai Prakhya" <[email protected]>
Cc: "Vikas Shivappa" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

Author: Fenghua Yu

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -194,12 +194,13 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 /*
  * This is safe against intel_rdt_sched_in() called from __switch_to()
  * because __switch_to() is executed with interrupts disabled. A local call
- * from rdt_update_percpu_closid() is proteced against __switch_to() because
+ * from rdt_update_closid() is proteced against __switch_to() because
  * preemption is disabled.
  */
-static void rdt_update_cpu_closid(void *v)
+static void rdt_update_cpu_closid(void *closid)
 {
-	this_cpu_write(cpu_closid, *(int *)v);
+	if (closid)
+		this_cpu_write(cpu_closid, *(int *)closid);
 	/*
 	 * We cannot unconditionally write the MSR because the current
 	 * executing task might have its own closid selected. Just reuse
@@ -208,14 +209,23 @@ static void rdt_update_cpu_closid(void *v)
 	intel_rdt_sched_in();
 }
 
-/* Update the per cpu closid and eventually the PGR_ASSOC MSR */
-static void rdt_update_percpu_closid(const struct cpumask *cpu_mask, int closid)
+/*
+ * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
+ *
+ * Per task closids must have been set up before calling this function.
+ *
+ * The per cpu closids are updated with the smp function call, when @closid
+ * is not NULL. If @closid is NULL then all affected percpu closids must
+ * have been set up before calling this function.
+ */
+static void
+rdt_update_closid(const struct cpumask *cpu_mask, int *closid)
 {
 	int cpu = get_cpu();
 
 	if (cpumask_test_cpu(cpu, cpu_mask))
-		rdt_update_cpu_closid(&closid);
-	smp_call_function_many(cpu_mask, rdt_update_cpu_closid, &closid, 1);
+		rdt_update_cpu_closid(closid);
+	smp_call_function_many(cpu_mask, rdt_update_cpu_closid, closid, 1);
 	put_cpu();
 }
 
@@ -264,7 +274,7 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		/* Give any dropped cpus to rdtgroup_default */
 		cpumask_or(&rdtgroup_default.cpu_mask,
 			   &rdtgroup_default.cpu_mask, tmpmask);
-		rdt_update_percpu_closid(tmpmask, rdtgroup_default.closid);
+		rdt_update_closid(tmpmask, &rdtgroup_default.closid);
 	}
 
 	/*
@@ -278,7 +288,7 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 				continue;
 			cpumask_andnot(&r->cpu_mask, &r->cpu_mask, tmpmask);
 		}
-		rdt_update_percpu_closid(tmpmask, rdtgrp->closid);
+		rdt_update_closid(tmpmask, &rdtgrp->closid);
 	}
 
 	/* Done pushing/pulling - update this group with new mask */
@@ -807,18 +817,49 @@ static int reset_all_cbms(struct rdt_resource *r)
 }
 
 /*
- * Forcibly remove all of subdirectories under root.
+ * Move tasks from one to the other group. If @from is NULL, then all tasks
+ * in the systems are moved unconditionally (used for teardown).
+ *
+ * If @mask is not NULL the cpus on which moved tasks are running are set
+ * in that mask so the update smp function call is restricted to affected
+ * cpus.
  */
-static void rmdir_all_sub(void)
+static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
+				 struct cpumask *mask)
 {
-	struct rdtgroup *rdtgrp, *tmp;
 	struct task_struct *p, *t;
 
-	/* move all tasks to default resource group */
 	read_lock(&tasklist_lock);
-	for_each_process_thread(p, t)
-		t->closid = 0;
+	for_each_process_thread(p, t) {
+		if (!from || t->closid == from->closid) {
+			t->closid = to->closid;
+#ifdef CONFIG_SMP
+			/*
+			 * This is safe on x86 w/o barriers as the ordering
+			 * of writing to task_cpu() and t->on_cpu is
+			 * reverse to the reading here. The detection is
+			 * inaccurate as tasks might move or schedule
+			 * before the smp function call takes place. In
+			 * such a case the function call is pointless, but
+			 * there is no other side effect.
+			 */
+			if (mask && t->on_cpu)
+				cpumask_set_cpu(task_cpu(t), mask);
+#endif
+		}
+	}
 	read_unlock(&tasklist_lock);
+}
+
+/*
+ * Forcibly remove all of subdirectories under root.
+ */
+static void rmdir_all_sub(void)
+{
+	struct rdtgroup *rdtgrp, *tmp;
+
+	/* Move all tasks to the default resource group */
+	rdt_move_group_tasks(NULL, &rdtgroup_default, NULL);
 
 	list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
 		/* Remove each rdtgroup other than root */
@@ -833,13 +874,15 @@ static void rmdir_all_sub(void)
 		cpumask_or(&rdtgroup_default.cpu_mask,
 			   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
 
-		rdt_update_percpu_closid(&rdtgrp->cpu_mask,
-					 rdtgroup_default.closid);
-
 		kernfs_remove(rdtgrp->kn);
 		list_del(&rdtgrp->rdtgroup_list);
 		kfree(rdtgrp);
 	}
+	/* Notify online CPUs to update per cpu storage and PQR_ASSOC MSR */
+	get_online_cpus();
+	rdt_update_closid(cpu_online_mask, &rdtgroup_default.closid);
+	put_online_cpus();
+
 	kernfs_remove(kn_info);
 }
 
@@ -944,27 +987,35 @@ static int rdtgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 
 static int rdtgroup_rmdir(struct kernfs_node *kn)
 {
-	struct task_struct *p, *t;
+	int ret, cpu, closid = rdtgroup_default.closid;
 	struct rdtgroup *rdtgrp;
+	cpumask_var_t tmpmask;
+
+	if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
+		return -ENOMEM;
 
 	rdtgrp = rdtgroup_kn_lock_live(kn);
 	if (!rdtgrp) {
-		rdtgroup_kn_unlock(kn);
-		return -EPERM;
+		ret = -EPERM;
+		goto out;
 	}
 
 	/* Give any tasks back to the default group */
-	read_lock(&tasklist_lock);
-	for_each_process_thread(p, t) {
-		if (t->closid == rdtgrp->closid)
-			t->closid = 0;
-	}
-	read_unlock(&tasklist_lock);
+	rdt_move_group_tasks(rdtgrp, &rdtgroup_default, tmpmask);
 
 	/* Give any CPUs back to the default group */
 	cpumask_or(&rdtgroup_default.cpu_mask,
 		   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
-	rdt_update_percpu_closid(&rdtgrp->cpu_mask, rdtgroup_default.closid);
+
+	/* Update per cpu closid of the moved CPUs first */
+	for_each_cpu(cpu, &rdtgrp->cpu_mask)
+		per_cpu(cpu_closid, cpu) = closid;
+	/*
+	 * Update the MSR on moved CPUs and CPUs which have moved
+	 * task running on them.
+	 */
+	cpumask_or(tmpmask, tmpmask, &rdtgrp->cpu_mask);
+	rdt_update_closid(tmpmask, NULL);
 
 	rdtgrp->flags = RDT_DELETED;
 	closid_free(rdtgrp->closid);
@@ -976,9 +1027,11 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
 	 */
 	kernfs_get(kn);
 	kernfs_remove(rdtgrp->kn);
-
+	ret = 0;
+out:
 	rdtgroup_kn_unlock(kn);
-	return 0;
+	free_cpumask_var(tmpmask);
+	return ret;
 }
 
 static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {