From: Fenghua Yu <fenghua...@intel.com>

The root directory all subdirectories are automatically populated
with a read/write (mode 0644) file named "tasks". When read it will
show all the task IDs assigned to the resource group. Tasks can be
added (one at a time) to a group by writing the task ID to the file.
E.g.

Membership in a resource group is indicated by a new field in the
task_struct "int closid" which holds the CLOSID for each task. The
default resource group uses CLOSID=0 which means that all existing
tasks when the resctrl file system is mounted belong to the default
group.

A resource group cannot be removed while there are tasks assigned
to it.

Signed-off-by: Fenghua Yu <fenghua...@intel.com>
Signed-off-by: Tony Luck <tony.l...@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 173 +++++++++++++++++++++++++++++++
 include/linux/sched.h                    |   3 +
 2 files changed, 176 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c 
b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index f2d7a3a..bdbe2d1 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -28,6 +28,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/cpu.h>
+#include <linux/task_work.h>
 
 #include <uapi/linux/magic.h>
 
@@ -278,6 +279,152 @@ unlock:
        return ret ?: nbytes;
 }
 
+struct task_move_callback {
+       struct callback_head work;
+       struct rdtgroup *rdtgrp;
+};
+
+static void move_myself(struct callback_head *head)
+{
+       struct task_move_callback *callback;
+       struct rdtgroup *rdtgrp;
+
+       callback = container_of(head, struct task_move_callback, work);
+       rdtgrp = callback->rdtgrp;
+
+       /* Resource group might have been deleted before process runs */
+       if (atomic_dec_and_test(&rdtgrp->waitcount) &&
+           (rdtgrp->flags & RDT_DELETED)) {
+               current->closid = 0;
+               kfree(rdtgrp);
+       }
+
+       kfree(callback);
+}
+
+static int __rdtgroup_move_task(struct task_struct *tsk,
+                               struct rdtgroup *rdtgrp)
+{
+       struct task_move_callback *callback;
+       int ret;
+
+       callback = kzalloc(sizeof(*callback), GFP_KERNEL);
+       if (!callback)
+               return -ENOMEM;
+       callback->work.func = move_myself;
+       callback->rdtgrp = rdtgrp;
+       atomic_inc(&rdtgrp->waitcount);
+       ret = task_work_add(tsk, &callback->work, true);
+       if (ret) {
+               atomic_dec(&rdtgrp->waitcount);
+               kfree(callback);
+       } else {
+               tsk->closid = rdtgrp->closid;
+       }
+       return ret;
+}
+
+static int rdtgroup_task_write_permission(struct task_struct *task,
+                                         struct kernfs_open_file *of)
+{
+       const struct cred *cred = current_cred();
+       const struct cred *tcred = get_task_cred(task);
+       int ret = 0;
+
+       /*
+        * even if we're attaching all tasks in the thread group, we only
+        * need to check permissions on one of them.
+        */
+       if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
+           !uid_eq(cred->euid, tcred->uid) &&
+           !uid_eq(cred->euid, tcred->suid))
+               ret = -EPERM;
+
+       put_cred(tcred);
+       return ret;
+}
+
+static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
+                             struct kernfs_open_file *of)
+{
+       struct task_struct *tsk;
+       int ret;
+
+       rcu_read_lock();
+       if (pid) {
+               tsk = find_task_by_vpid(pid);
+               if (!tsk) {
+                       ret = -ESRCH;
+                       goto out_unlock_rcu;
+               }
+       } else {
+               tsk = current;
+       }
+
+       get_task_struct(tsk);
+       rcu_read_unlock();
+
+       ret = rdtgroup_task_write_permission(tsk, of);
+       if (!ret)
+               ret = __rdtgroup_move_task(tsk, rdtgrp);
+
+       put_task_struct(tsk);
+       return ret;
+
+out_unlock_rcu:
+       rcu_read_unlock();
+       return ret;
+}
+
+static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
+                                   char *buf, size_t nbytes, loff_t off)
+{
+       struct rdtgroup *rdtgrp;
+       pid_t pid;
+       int ret = 0;
+
+       if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+               return -EINVAL;
+       rdtgrp = rdtgroup_kn_lock_live(of->kn);
+
+       if (rdtgrp)
+               ret = rdtgroup_move_task(pid, rdtgrp, of);
+       else
+               ret = -ENOENT;
+
+       rdtgroup_kn_unlock(of->kn);
+
+       return ret ?: nbytes;
+}
+
+static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
+{
+       struct task_struct *p;
+
+       rcu_read_lock();
+       for_each_process(p) {
+               if (p->closid == r->closid)
+                       seq_printf(s, "%d\n", p->pid);
+       }
+       rcu_read_unlock();
+}
+
+static int rdtgroup_tasks_show(struct kernfs_open_file *of,
+                              struct seq_file *s, void *v)
+{
+       struct rdtgroup *rdtgrp;
+       int ret = 0;
+
+       rdtgrp = rdtgroup_kn_lock_live(of->kn);
+       if (rdtgrp)
+               show_rdt_tasks(rdtgrp, s);
+       else
+               ret = -ENOENT;
+       rdtgroup_kn_unlock(of->kn);
+
+       return ret;
+}
+
 /* Files in each rdtgroup */
 static struct rftype rdtgroup_base_files[] = {
        {
@@ -288,6 +435,13 @@ static struct rftype rdtgroup_base_files[] = {
                .seq_show       = rdtgroup_cpus_show,
        },
        {
+               .name           = "tasks",
+               .mode           = 0644,
+               .kf_ops         = &rdtgroup_kf_single_ops,
+               .write          = rdtgroup_tasks_write,
+               .seq_show       = rdtgroup_tasks_show,
+       },
+       {
                /* NULL terminated */
        }
 };
@@ -559,6 +713,13 @@ static void rmdir_all_sub(void)
 {
        struct rdtgroup *rdtgrp;
        struct list_head *l, *next;
+       struct task_struct *p;
+
+       /* move all tasks to default resource group */
+       read_lock(&tasklist_lock);
+       for_each_process(p)
+               p->closid = 0;
+       read_unlock(&tasklist_lock);
 
        get_cpu();
        /* Reset PQR_ASSOC MSR on this cpu. */
@@ -681,6 +842,7 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
 {
        struct rdtgroup *rdtgrp;
        int ret = 0;
+       struct task_struct *p;
 
        rdtgrp = rdtgroup_kn_lock_live(kn);
        if (!rdtgrp) {
@@ -698,6 +860,17 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
                return -EPERM;
        }
 
+       /* Don't allow if there are processes in this group */
+       read_lock(&tasklist_lock);
+       for_each_process(p) {
+               if (p->closid == rdtgrp->closid) {
+                       read_unlock(&tasklist_lock);
+                       rdtgroup_kn_unlock(kn);
+                       return -EBUSY;
+               }
+       }
+       read_unlock(&tasklist_lock);
+
        /* Give any CPUs back to the default group */
        cpumask_or(&rdtgroup_default.cpu_mask,
                   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 62c68e5..8a05c46 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1766,6 +1766,9 @@ struct task_struct {
        /* cg_list protected by css_set_lock and tsk->alloc_lock */
        struct list_head cg_list;
 #endif
+#ifdef CONFIG_INTEL_RDT_A
+       int closid;
+#endif
 #ifdef CONFIG_FUTEX
        struct robust_list_head __user *robust_list;
 #ifdef CONFIG_COMPAT
-- 
2.5.0

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