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>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7868fc3c0bc59b3223490114ca8e27f83b4c864c..a46d7e2012b4db7d63eb794833f24c048c2b6c57 100644 (file)
--- 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;