cgroup: restructure child_subsys_mask handling in cgroup_subtree_control_write()

Make cgroup_subtree_control_write() first calculate new
subtree_control (new_sc), child_subsys_mask (new_ss) and
css_enable/disable masks before applying them to the cgroup.  Also,
store the original subtree_control (old_sc) and child_subsys_mask
(old_ss) and use them to restore the orignal state after failure.

This patch shouldn't cause any behavior changes.  This prepares for a
fix for a bug in the async css offline wait logic.

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

1 files changed, 12 insertions, 12 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1dda601ec337..cbbb46f783de 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2653,7 +2653,7 @@ 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;
@@ -2770,18 +2770,19 @@ 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;
 
+        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
@@ -2844,9 +2845,8 @@ 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)))