1 files changed, 20 insertions, 57 deletions

diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
index cdd8df4e991c..b50d5a167fda 100644
--- a/kernel/cgroup_pids.c
+++ b/kernel/cgroup_pids.c
@@ -106,7 +106,7 @@ static void pids_uncharge(struct pids_cgroup *pids, int num)
 {
         struct pids_cgroup *p;
 
-        for (p = pids; p; p = parent_pids(p))
+        for (p = pids; parent_pids(p); p = parent_pids(p))
                 pids_cancel(p, num);
 }
 
@@ -123,7 +123,7 @@ static void pids_charge(struct pids_cgroup *pids, int num)
 {
         struct pids_cgroup *p;
 
-        for (p = pids; p; p = parent_pids(p))
+        for (p = pids; parent_pids(p); p = parent_pids(p))
                 atomic64_add(num, &p->counter);
 }
 
@@ -140,7 +140,7 @@ static int pids_try_charge(struct pids_cgroup *pids, int num)
 {
         struct pids_cgroup *p, *q;
 
-        for (p = pids; p; p = parent_pids(p)) {
+        for (p = pids; parent_pids(p); p = parent_pids(p)) {
                 int64_t new = atomic64_add_return(num, &p->counter);
 
                 /*
@@ -162,13 +162,13 @@ revert:
         return -EAGAIN;
 }
 
-static int pids_can_attach(struct cgroup_subsys_state *css,
-                           struct cgroup_taskset *tset)
+static int pids_can_attach(struct cgroup_taskset *tset)
 {
-        struct pids_cgroup *pids = css_pids(css);
         struct task_struct *task;
+        struct cgroup_subsys_state *dst_css;
 
-        cgroup_taskset_for_each(task, tset) {
+        cgroup_taskset_for_each(task, dst_css, tset) {
+                struct pids_cgroup *pids = css_pids(dst_css);
                 struct cgroup_subsys_state *old_css;
                 struct pids_cgroup *old_pids;
 
@@ -187,13 +187,13 @@ static int pids_can_attach(struct cgroup_subsys_state *css,
         return 0;
 }
 
-static void pids_cancel_attach(struct cgroup_subsys_state *css,
-                               struct cgroup_taskset *tset)
+static void pids_cancel_attach(struct cgroup_taskset *tset)
 {
-        struct pids_cgroup *pids = css_pids(css);
         struct task_struct *task;
+        struct cgroup_subsys_state *dst_css;
 
-        cgroup_taskset_for_each(task, tset) {
+        cgroup_taskset_for_each(task, dst_css, tset) {
+                struct pids_cgroup *pids = css_pids(dst_css);
                 struct cgroup_subsys_state *old_css;
                 struct pids_cgroup *old_pids;
 
@@ -205,65 +205,28 @@ static void pids_cancel_attach(struct cgroup_subsys_state *css,
         }
 }
 
+/*
+ * task_css_check(true) in pids_can_fork() and pids_cancel_fork() relies
+ * on threadgroup_change_begin() held by the copy_process().
+ */
 static int pids_can_fork(struct task_struct *task, void **priv_p)
 {
         struct cgroup_subsys_state *css;
         struct pids_cgroup *pids;
-        int err;
 
-        /*
-         * Use the "current" task_css for the pids subsystem as the tentative
-         * css. It is possible we will charge the wrong hierarchy, in which
-         * case we will forcefully revert/reapply the charge on the right
-         * hierarchy after it is committed to the task proper.
-         */
-        css = task_get_css(current, pids_cgrp_id);
+        css = task_css_check(current, pids_cgrp_id, true);
         pids = css_pids(css);
-
-        err = pids_try_charge(pids, 1);
-        if (err)
-                goto err_css_put;
-
-        *priv_p = css;
-        return 0;
-
-err_css_put:
-        css_put(css);
-        return err;
+        return pids_try_charge(pids, 1);
 }
 
 static void pids_cancel_fork(struct task_struct *task, void *priv)
 {
-        struct cgroup_subsys_state *css = priv;
-        struct pids_cgroup *pids = css_pids(css);
-
-        pids_uncharge(pids, 1);
-        css_put(css);
-}
-
-static void pids_fork(struct task_struct *task, void *priv)
-{
         struct cgroup_subsys_state *css;
-        struct cgroup_subsys_state *old_css = priv;
         struct pids_cgroup *pids;
-        struct pids_cgroup *old_pids = css_pids(old_css);
 
-        css = task_get_css(task, pids_cgrp_id);
+        css = task_css_check(current, pids_cgrp_id, true);
         pids = css_pids(css);
-
-        /*
-         * If the association has changed, we have to revert and reapply the
-         * charge/uncharge on the wrong hierarchy to the current one. Since
-         * the association can only change due to an organisation event, its
-         * okay for us to ignore the limit in this case.
-         */
-        if (pids != old_pids) {
-                pids_uncharge(old_pids, 1);
-                pids_charge(pids, 1);
-        }
-
-        css_put(css);
-        css_put(old_css);
+        pids_uncharge(pids, 1);
 }
 
 static void pids_free(struct task_struct *task)
@@ -335,6 +298,7 @@ static struct cftype pids_files[] = {
         {
                 .name = "current",
                 .read_s64 = pids_current_read,
+                .flags = CFTYPE_NOT_ON_ROOT,
         },
         { }     /* terminate */
 };
@@ -346,7 +310,6 @@ struct cgroup_subsys pids_cgrp_subsys = {
         .cancel_attach  = pids_cancel_attach,
         .can_fork       = pids_can_fork,
         .cancel_fork    = pids_cancel_fork,
-        .fork           = pids_fork,
         .free           = pids_free,
         .legacy_cftypes = pids_files,
         .dfl_cftypes    = pids_files,