7 files changed, 30 insertions, 22 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 308b10797a54..cae5831ae650 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -36,9 +36,13 @@
 #define CGROUP_WEIGHT_DFL               100
 #define CGROUP_WEIGHT_MAX               10000
 
+/* walk only threadgroup leaders */
+#define CSS_TASK_ITER_PROCS             (1U << 0)
+
 /* a css_task_iter should be treated as an opaque object */
 struct css_task_iter {
         struct cgroup_subsys            *ss;
+        unsigned int                    flags;
 
         struct list_head                *cset_pos;
         struct list_head                *cset_head;
@@ -129,7 +133,7 @@ struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
                                         struct cgroup_subsys_state **dst_cssp);
 
-void css_task_iter_start(struct cgroup_subsys_state *css,
+void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
                          struct css_task_iter *it);
 struct task_struct *css_task_iter_next(struct css_task_iter *it);
 void css_task_iter_end(struct css_task_iter *it);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 60f72475863e..167aaab04bf9 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -121,7 +121,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
          * ->can_attach() fails.
          */
         do {
-                css_task_iter_start(&from->self, &it);
+                css_task_iter_start(&from->self, 0, &it);
                 task = css_task_iter_next(&it);
                 if (task)
                         get_task_struct(task);
@@ -373,7 +373,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
         if (!array)
                 return -ENOMEM;
         /* now, populate the array */
-        css_task_iter_start(&cgrp->self, &it);
+        css_task_iter_start(&cgrp->self, 0, &it);
         while ((tsk = css_task_iter_next(&it))) {
                 if (unlikely(n == length))
                         break;
@@ -749,7 +749,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
         }
         rcu_read_unlock();
 
-        css_task_iter_start(&cgrp->self, &it);
+        css_task_iter_start(&cgrp->self, 0, &it);
         while ((tsk = css_task_iter_next(&it))) {
                 switch (tsk->state) {
                 case TASK_RUNNING:
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index e3bda0752501..3c5a37a9a892 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3643,6 +3643,7 @@ static void css_task_iter_advance(struct css_task_iter *it)
         lockdep_assert_held(&css_set_lock);
         WARN_ON_ONCE(!l);
 
+repeat:
         /*
          * Advance iterator to find next entry.  cset->tasks is consumed
          * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
@@ -3657,11 +3658,18 @@ static void css_task_iter_advance(struct css_task_iter *it)
                 css_task_iter_advance_css_set(it);
         else
                 it->task_pos = l;
+
+        /* if PROCS, skip over tasks which aren't group leaders */
+        if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
+            !thread_group_leader(list_entry(it->task_pos, struct task_struct,
+                                            cg_list)))
+                goto repeat;
 }
 
 /**
  * css_task_iter_start - initiate task iteration
  * @css: the css to walk tasks of
+ * @flags: CSS_TASK_ITER_* flags
  * @it: the task iterator to use
  *
  * Initiate iteration through the tasks of @css.  The caller can call
@@ -3669,7 +3677,7 @@ static void css_task_iter_advance(struct css_task_iter *it)
  * returns NULL.  On completion of iteration, css_task_iter_end() must be
  * called.
  */
-void css_task_iter_start(struct cgroup_subsys_state *css,
+void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
                          struct css_task_iter *it)
 {
         /* no one should try to iterate before mounting cgroups */
@@ -3680,6 +3688,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css,
         spin_lock_irq(&css_set_lock);
 
         it->ss = css->ss;
+        it->flags = flags;
 
         if (it->ss)
                 it->cset_pos = &css->cgroup->e_csets[css->ss->id];
@@ -3753,13 +3762,8 @@ static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
 {
         struct kernfs_open_file *of = s->private;
         struct css_task_iter *it = of->priv;
-        struct task_struct *task;
-
-        do {
-                task = css_task_iter_next(it);
-        } while (task && !thread_group_leader(task));
 
-        return task;
+        return css_task_iter_next(it);
 }
 
 static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
@@ -3780,10 +3784,10 @@ static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
                 if (!it)
                         return ERR_PTR(-ENOMEM);
                 of->priv = it;
-                css_task_iter_start(&cgrp->self, it);
+                css_task_iter_start(&cgrp->self, CSS_TASK_ITER_PROCS, it);
         } else if (!(*pos)++) {
                 css_task_iter_end(it);
-                css_task_iter_start(&cgrp->self, it);
+                css_task_iter_start(&cgrp->self, CSS_TASK_ITER_PROCS, it);
         }
 
         return cgroup_procs_next(s, NULL, NULL);
@@ -3791,7 +3795,7 @@ static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
 
 static int cgroup_procs_show(struct seq_file *s, void *v)
 {
-        seq_printf(s, "%d\n", task_tgid_vnr(v));
+        seq_printf(s, "%d\n", task_pid_vnr(v));
         return 0;
 }
 
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ca8376e5008c..252d70c9a49b 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -861,7 +861,7 @@ static void update_tasks_cpumask(struct cpuset *cs)
         struct css_task_iter it;
         struct task_struct *task;
 
-        css_task_iter_start(&cs->css, &it);
+        css_task_iter_start(&cs->css, 0, &it);
         while ((task = css_task_iter_next(&it)))
                 set_cpus_allowed_ptr(task, cs->effective_cpus);
         css_task_iter_end(&it);
@@ -1091,7 +1091,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
          * It's ok if we rebind the same mm twice; mpol_rebind_mm()
          * is idempotent.  Also migrate pages in each mm to new nodes.
          */
-        css_task_iter_start(&cs->css, &it);
+        css_task_iter_start(&cs->css, 0, &it);
         while ((task = css_task_iter_next(&it))) {
                 struct mm_struct *mm;
                 bool migrate;
@@ -1284,7 +1284,7 @@ static void update_tasks_flags(struct cpuset *cs)
         struct css_task_iter it;
         struct task_struct *task;
 
-        css_task_iter_start(&cs->css, &it);
+        css_task_iter_start(&cs->css, 0, &it);
         while ((task = css_task_iter_next(&it)))
                 cpuset_update_task_spread_flag(cs, task);
         css_task_iter_end(&it);
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index 1b72d56edce5..08236798d173 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -268,7 +268,7 @@ static void update_if_frozen(struct cgroup_subsys_state *css)
         rcu_read_unlock();
 
         /* are all tasks frozen? */
-        css_task_iter_start(css, &it);
+        css_task_iter_start(css, 0, &it);
 
         while ((task = css_task_iter_next(&it))) {
                 if (freezing(task)) {
@@ -320,7 +320,7 @@ static void freeze_cgroup(struct freezer *freezer)
         struct css_task_iter it;
         struct task_struct *task;
 
-        css_task_iter_start(&freezer->css, &it);
+        css_task_iter_start(&freezer->css, 0, &it);
         while ((task = css_task_iter_next(&it)))
                 freeze_task(task);
         css_task_iter_end(&it);
@@ -331,7 +331,7 @@ static void unfreeze_cgroup(struct freezer *freezer)
         struct css_task_iter it;
         struct task_struct *task;
 
-        css_task_iter_start(&freezer->css, &it);
+        css_task_iter_start(&freezer->css, 0, &it);
         while ((task = css_task_iter_next(&it)))
                 __thaw_task(task);
         css_task_iter_end(&it);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3df3c04d73ab..2b2f071f914b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -917,7 +917,7 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
                 struct css_task_iter it;
                 struct task_struct *task;
 
-                css_task_iter_start(&iter->css, &it);
+                css_task_iter_start(&iter->css, 0, &it);
                 while (!ret && (task = css_task_iter_next(&it)))
                         ret = fn(task, arg);
                 css_task_iter_end(&it);
diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index 029a61ac6cdd..5e4f04004a49 100644
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -100,7 +100,7 @@ static int write_classid(struct cgroup_subsys_state *css, struct cftype *cft,
 
         cs->classid = (u32)value;
 
-        css_task_iter_start(css, &it);
+        css_task_iter_start(css, 0, &it);
         while ((p = css_task_iter_next(&it))) {
                 task_lock(p);
                 iterate_fd(p->files, 0, update_classid_sock,