cgroup: factor out cgroup_apply_control_disable() from cgroup_subtree_control_write()

Factor out css disabling and hiding into cgroup_apply_control_disable().

* Nest subsystem walk inside child walk.  The child walk will later be
  converted to subtree walk which is a bit more expensive.

* Instead of operating on the differential masks @css_enable and
  @css_disable, simply disable or hide csses according to the current
  cgroup_control() and cgroup_ss_mask().  This leads to the same
  result and is simpler and more robust.

* This allows error handling path to share the same code.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d295e6a..97cb131 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3012,6 +3012,43 @@ static bool cgroup_drain_offline(struct cgroup *cgrp)
        return false;
 }
 
+/**
+ * cgroup_apply_control_disable - kill or hide csses according to control
+ * @cgrp: parent of the target cgroups
+ *
+ * Walk @cgrp's children and kill and hide csses so that they match
+ * cgroup_ss_mask() and cgroup_visible_mask().
+ *
+ * A css is hidden when the userland requests it to be disabled while other
+ * subsystems are still depending on it.  The css must not actively control
+ * resources and be in the vanilla state if it's made visible again later.
+ * Controllers which may be depended upon should provide ->css_reset() for
+ * this purpose.
+ */
+static void cgroup_apply_control_disable(struct cgroup *cgrp)
+{
+       struct cgroup *dsct;
+       struct cgroup_subsys *ss;
+       int ssid;
+
+       cgroup_for_each_live_child(dsct, cgrp) {
+               for_each_subsys(ss, ssid) {
+                       struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
+
+                       if (!css)
+                               continue;
+
+                       if (!(cgroup_ss_mask(dsct) & (1 << ss->id))) {
+                               kill_css(css);
+                       } else if (!(cgroup_control(dsct) & (1 << ss->id))) {
+                               css_clear_dir(css, NULL);
+                               if (ss->css_reset)
+                                       ss->css_reset(css);
+                       }
+               }
+       }
+}
+
 /* change the enabled child controllers for a cgroup in the default hierarchy */
 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                            char *buf, size_t nbytes,
@@ -3160,27 +3197,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
        if (ret)
                goto err_undo_css;
 
-       /*
-        * All tasks are migrated out of disabled csses.  Kill or hide
-        * them.  A css is hidden when the userland requests it to be
-        * disabled while other subsystems are still depending on it.  The
-        * css must not actively control resources and be in the vanilla
-        * state if it's made visible again later.  Controllers which may
-        * be depended upon should provide ->css_reset() for this purpose.
-        */
-       do_each_subsys_mask(ss, ssid, disable) {
-               cgroup_for_each_live_child(child, cgrp) {
-                       struct cgroup_subsys_state *css = cgroup_css(child, ss);
-
-                       if (css_disable & (1 << ssid)) {
-                               kill_css(css);
-                       } else {
-                               css_clear_dir(css, NULL);
-                               if (ss->css_reset)
-                                       ss->css_reset(css);
-                       }
-               }
-       } while_each_subsys_mask();
+       /* all tasks are migrated out of disabled csses, commit disable */
+       cgroup_apply_control_disable(cgrp);
 
        kernfs_activate(cgrp->kn);
        ret = 0;
@@ -3189,22 +3207,12 @@ out_unlock:
        return ret ?: nbytes;
 
 err_undo_css:
+       /* restore masks and shoot down new csses */
        cgrp->subtree_control = old_sc;
        cgrp->subtree_ss_mask = old_ss;
 
-       do_each_subsys_mask(ss, ssid, enable) {
-               cgroup_for_each_live_child(child, cgrp) {
-                       struct cgroup_subsys_state *css = cgroup_css(child, ss);
-
-                       if (!css)
-                               continue;
+       cgroup_apply_control_disable(cgrp);
 
-                       if (css_enable & (1 << ssid))
-                               kill_css(css);
-                       else
-                               css_clear_dir(css, NULL);
-               }
-       } while_each_subsys_mask();
        goto out_unlock;
 }