1 files changed, 121 insertions, 54 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 136eceadeed1..bb263d0caab3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -277,6 +277,10 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
         if (!(cgrp->root->subsys_mask & (1 << ss->id)))
                 return NULL;
 
+        /*
+         * This function is used while updating css associations and thus
+         * can't test the csses directly.  Use ->child_subsys_mask.
+         */
         while (cgroup_parent(cgrp) &&
                !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id)))
                 cgrp = cgroup_parent(cgrp);
@@ -284,6 +288,39 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
         return cgroup_css(cgrp, ss);
 }
 
+/**
+ * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest
+ *
+ * Find and get the effective css of @cgrp for @ss.  The effective css is
+ * defined as the matching css of the nearest ancestor including self which
+ * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
+ * the root css is returned, so this function always returns a valid css.
+ * The returned css must be put using css_put().
+ */
+struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
+                                             struct cgroup_subsys *ss)
+{
+        struct cgroup_subsys_state *css;
+
+        rcu_read_lock();
+
+        do {
+                css = cgroup_css(cgrp, ss);
+
+                if (css && css_tryget_online(css))
+                        goto out_unlock;
+                cgrp = cgroup_parent(cgrp);
+        } while (cgrp);
+
+        css = init_css_set.subsys[ss->id];
+        css_get(css);
+out_unlock:
+        rcu_read_unlock();
+        return css;
+}
+
 /* convenient tests for these bits */
 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 {
@@ -1019,31 +1056,30 @@ static void cgroup_put(struct cgroup *cgrp)
 }
 
 /**
- * cgroup_refresh_child_subsys_mask - update child_subsys_mask
+ * cgroup_calc_child_subsys_mask - calculate child_subsys_mask
  * @cgrp: the target cgroup
+ * @subtree_control: the new subtree_control mask to consider
  *
  * On the default hierarchy, a subsystem may request other subsystems to be
  * enabled together through its ->depends_on mask.  In such cases, more
  * subsystems than specified in "cgroup.subtree_control" may be enabled.
  *
- * This function determines which subsystems need to be enabled given the
- * current @cgrp->subtree_control and records it in
- * @cgrp->child_subsys_mask.  The resulting mask is always a superset of
- * @cgrp->subtree_control and follows the usual hierarchy rules.
+ * This function calculates which subsystems need to be enabled if
+ * @subtree_control is to be applied to @cgrp.  The returned mask is always
+ * a superset of @subtree_control and follows the usual hierarchy rules.
  */
-static void cgroup_refresh_child_subsys_mask(struct cgroup *cgrp)
+static unsigned int cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
+                                                  unsigned int subtree_control)
 {
         struct cgroup *parent = cgroup_parent(cgrp);
-        unsigned int cur_ss_mask = cgrp->subtree_control;
+        unsigned int cur_ss_mask = subtree_control;
         struct cgroup_subsys *ss;
         int ssid;
 
         lockdep_assert_held(&cgroup_mutex);
 
-        if (!cgroup_on_dfl(cgrp)) {
-                cgrp->child_subsys_mask = cur_ss_mask;
-                return;
-        }
+        if (!cgroup_on_dfl(cgrp))
+                return cur_ss_mask;
 
         while (true) {
                 unsigned int new_ss_mask = cur_ss_mask;
@@ -1067,7 +1103,20 @@ static void cgroup_refresh_child_subsys_mask(struct cgroup *cgrp)
                 cur_ss_mask = new_ss_mask;
         }
 
-        cgrp->child_subsys_mask = cur_ss_mask;
+        return cur_ss_mask;
+}
+
+/**
+ * cgroup_refresh_child_subsys_mask - update child_subsys_mask
+ * @cgrp: the target cgroup
+ *
+ * Update @cgrp->child_subsys_mask according to the current
+ * @cgrp->subtree_control using cgroup_calc_child_subsys_mask().
+ */
+static void cgroup_refresh_child_subsys_mask(struct cgroup *cgrp)
+{
+        cgrp->child_subsys_mask =
+                cgroup_calc_child_subsys_mask(cgrp, cgrp->subtree_control);
 }
 
 /**
@@ -2641,7 +2690,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                             loff_t off)
 {
         unsigned int enable = 0, disable = 0;
-        unsigned int css_enable, css_disable, old_ctrl, new_ctrl;
+        unsigned int css_enable, css_disable, old_sc, new_sc, old_ss, new_ss;
         struct cgroup *cgrp, *child;
         struct cgroup_subsys *ss;
         char *tok;
@@ -2693,36 +2742,6 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                 ret = -ENOENT;
                                 goto out_unlock;
                         }
-
-                        /*
-                         * @ss is already enabled through dependency and
-                         * we'll just make it visible.  Skip draining.
-                         */
-                        if (cgrp->child_subsys_mask & (1 << ssid))
-                                continue;
-
-                        /*
-                         * Because css offlining is asynchronous, userland
-                         * might try to re-enable the same controller while
-                         * the previous instance is still around.  In such
-                         * cases, wait till it's gone using offline_waitq.
-                         */
-                        cgroup_for_each_live_child(child, cgrp) {
-                                DEFINE_WAIT(wait);
-
-                                if (!cgroup_css(child, ss))
-                                        continue;
-
-                                cgroup_get(child);
-                                prepare_to_wait(&child->offline_waitq, &wait,
-                                                TASK_UNINTERRUPTIBLE);
-                                cgroup_kn_unlock(of->kn);
-                                schedule();
-                                finish_wait(&child->offline_waitq, &wait);
-                                cgroup_put(child);
-
-                                return restart_syscall();
-                        }
                 } else if (disable & (1 << ssid)) {
                         if (!(cgrp->subtree_control & (1 << ssid))) {
                                 disable &= ~(1 << ssid);
@@ -2758,19 +2777,48 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
          * subsystems than specified may need to be enabled or disabled
          * depending on subsystem dependencies.
          */
-        cgrp->subtree_control |= enable;
-        cgrp->subtree_control &= ~disable;
+        old_sc = cgrp->subtree_control;
+        old_ss = cgrp->child_subsys_mask;
+        new_sc = (old_sc | enable) & ~disable;
+        new_ss = cgroup_calc_child_subsys_mask(cgrp, new_sc);
 
-        old_ctrl = cgrp->child_subsys_mask;
-        cgroup_refresh_child_subsys_mask(cgrp);
-        new_ctrl = cgrp->child_subsys_mask;
-
-        css_enable = ~old_ctrl & new_ctrl;
-        css_disable = old_ctrl & ~new_ctrl;
+        css_enable = ~old_ss & new_ss;
+        css_disable = old_ss & ~new_ss;
         enable |= css_enable;
         disable |= css_disable;
 
         /*
+         * Because css offlining is asynchronous, userland might try to
+         * re-enable the same controller while the previous instance is
+         * still around.  In such cases, wait till it's gone using
+         * offline_waitq.
+         */
+        for_each_subsys(ss, ssid) {
+                if (!(css_enable & (1 << ssid)))
+                        continue;
+
+                cgroup_for_each_live_child(child, cgrp) {
+                        DEFINE_WAIT(wait);
+
+                        if (!cgroup_css(child, ss))
+                                continue;
+
+                        cgroup_get(child);
+                        prepare_to_wait(&child->offline_waitq, &wait,
+                                        TASK_UNINTERRUPTIBLE);
+                        cgroup_kn_unlock(of->kn);
+                        schedule();
+                        finish_wait(&child->offline_waitq, &wait);
+                        cgroup_put(child);
+
+                        return restart_syscall();
+                }
+        }
+
+        cgrp->subtree_control = new_sc;
+        cgrp->child_subsys_mask = new_ss;
+
+        /*
          * Create new csses or make the existing ones visible.  A css is
          * created invisible if it's being implicitly enabled through
          * dependency.  An invisible css is made visible when the userland
@@ -2825,6 +2873,24 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                 }
         }
 
+        /*
+         * The effective csses of all the descendants (excluding @cgrp) may
+         * have changed.  Subsystems can optionally subscribe to this event
+         * by implementing ->css_e_css_changed() which is invoked if any of
+         * the effective csses seen from the css's cgroup may have changed.
+         */
+        for_each_subsys(ss, ssid) {
+                struct cgroup_subsys_state *this_css = cgroup_css(cgrp, ss);
+                struct cgroup_subsys_state *css;
+
+                if (!ss->css_e_css_changed || !this_css)
+                        continue;
+
+                css_for_each_descendant_pre(css, this_css)
+                        if (css != this_css)
+                                ss->css_e_css_changed(css);
+        }
+
         kernfs_activate(cgrp->kn);
         ret = 0;
 out_unlock:
@@ -2832,9 +2898,8 @@ out_unlock:
         return ret ?: nbytes;
 
 err_undo_css:
-        cgrp->subtree_control &= ~enable;
-        cgrp->subtree_control |= disable;
-        cgroup_refresh_child_subsys_mask(cgrp);
+        cgrp->subtree_control = old_sc;
+        cgrp->child_subsys_mask = old_ss;
 
         for_each_subsys(ss, ssid) {
                 if (!(enable & (1 << ssid)))
@@ -4370,6 +4435,8 @@ static void css_release_work_fn(struct work_struct *work)
         if (ss) {
                 /* css release path */
                 cgroup_idr_remove(&ss->css_idr, css->id);
+                if (ss->css_released)
+                        ss->css_released(css);
         } else {
                 /* cgroup release path */
                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);