cgroup: reorganize cgroup_subtree_control_write()

Make the following two reorganizations to
cgroup_subtree_control_write().  These are to prepare for future
changes and shouldn't cause any functional difference.

* Move availability above css offlining wait.

* Move cgrp->child_subsys_mask update above new css creation.

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

1 files changed, 17 insertions, 17 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7868fc3c0bc5..a46d7e2012b4 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2613,6 +2613,14 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                 continue;
                         }
 
+                        /* unavailable or not enabled on the parent? */
+                        if (!(cgrp_dfl_root.subsys_mask & (1 << ssid)) ||
+                            (cgroup_parent(cgrp) &&
+                             !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ssid)))) {
+                                ret = -ENOENT;
+                                goto out_unlock;
+                        }
+
                         /*
                          * Because css offlining is asynchronous, userland
                          * might try to re-enable the same controller while
@@ -2635,14 +2643,6 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 
                                 return restart_syscall();
                         }
-
-                        /* unavailable or not enabled on the parent? */
-                        if (!(cgrp_dfl_root.subsys_mask & (1 << ssid)) ||
-                            (cgroup_parent(cgrp) &&
-                             !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ssid)))) {
-                                ret = -ENOENT;
-                                goto out_unlock;
-                        }
                 } else if (disable & (1 << ssid)) {
                         if (!(cgrp->child_subsys_mask & (1 << ssid))) {
                                 disable &= ~(1 << ssid);
@@ -2673,12 +2673,10 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                 goto out_unlock;
         }
 
-        /*
-         * Create csses for enables and update child_subsys_mask.  This
-         * changes cgroup_e_css() results which in turn makes the
-         * subsequent cgroup_update_dfl_csses() associate all tasks in the
-         * subtree to the updated csses.
-         */
+        cgrp->child_subsys_mask |= enable;
+        cgrp->child_subsys_mask &= ~disable;
+
+        /* create new csses */
         for_each_subsys(ss, ssid) {
                 if (!(enable & (1 << ssid)))
                         continue;
@@ -2690,9 +2688,11 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                 }
         }
 
-        cgrp->child_subsys_mask |= enable;
-        cgrp->child_subsys_mask &= ~disable;
-
+        /*
+         * At this point, cgroup_e_css() results reflect the new csses
+         * making the following cgroup_update_dfl_csses() properly update
+         * css associations of all tasks in the subtree.
+         */
         ret = cgroup_update_dfl_csses(cgrp);
         if (ret)
                 goto err_undo_css;