cgroup: introduce cgroup->subtree_control

cgroup is implementing support for subsystem dependency which would
require a way to enable a subsystem even when it's not directly
configured through "cgroup.subtree_control".

Previously, cgroup->child_subsys_mask directly reflected
"cgroup.subtree_control" and the enabled subsystems in the child
cgroups.  This patch adds cgroup->subtree_control which
"cgroup.subtree_control" operates on.  cgroup->child_subsys_mask is
now calculated from cgroup->subtree_control by
cgroup_refresh_child_subsys_mask(), which sets it identical to
cgroup->subtree_control for now.

This will allow using cgroup->child_subsys_mask for all the enabled
subsystems including the implicit ones and ->subtree_control for
tracking the explicitly requested ones.  This patch keeps the two
masks identical and doesn't introduce any behavior changes.

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/include/linux/cgroup.h b/include/linux/cgroup.h
index 8a111dd..8d52c8e 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -203,7 +203,13 @@ struct cgroup {
        struct kernfs_node *kn;         /* cgroup kernfs entry */
        struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */
 
-       /* the bitmask of subsystems enabled on the child cgroups */
+       /*
+        * The bitmask of subsystems enabled on the child cgroups.
+        * ->subtree_control is the one configured through
+        * "cgroup.subtree_control" while ->child_subsys_mask is the
+        * effective one which may have more subsystems enabled.
+        */
+       unsigned int subtree_control;
        unsigned int child_subsys_mask;
 
        /* Private pointers for each registered subsystem */

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a46d7e2..14a9d88 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1036,6 +1036,11 @@ static void cgroup_put(struct cgroup *cgrp)
        css_put(&cgrp->self);
 }
 
+static void cgroup_refresh_child_subsys_mask(struct cgroup *cgrp)
+{
+       cgrp->child_subsys_mask = cgrp->subtree_control;
+}
+
 /**
  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
  * @kn: the kernfs_node being serviced
@@ -1208,12 +1213,15 @@ static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask)
                up_write(&css_set_rwsem);
 
                src_root->subsys_mask &= ~(1 << ssid);
-               src_root->cgrp.child_subsys_mask &= ~(1 << ssid);
+               src_root->cgrp.subtree_control &= ~(1 << ssid);
+               cgroup_refresh_child_subsys_mask(&src_root->cgrp);
 
                /* default hierarchy doesn't enable controllers by default */
                dst_root->subsys_mask |= 1 << ssid;
-               if (dst_root != &cgrp_dfl_root)
-                       dst_root->cgrp.child_subsys_mask |= 1 << ssid;
+               if (dst_root != &cgrp_dfl_root) {
+                       dst_root->cgrp.subtree_control |= 1 << ssid;
+                       cgroup_refresh_child_subsys_mask(&dst_root->cgrp);
+               }
 
                if (ss->bind)
                        ss->bind(css);
@@ -2454,7 +2462,7 @@ static int cgroup_controllers_show(struct seq_file *seq, void *v)
 {
        struct cgroup *cgrp = seq_css(seq)->cgroup;
 
-       cgroup_print_ss_mask(seq, cgroup_parent(cgrp)->child_subsys_mask);
+       cgroup_print_ss_mask(seq, cgroup_parent(cgrp)->subtree_control);
        return 0;
 }
 
@@ -2463,7 +2471,7 @@ static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
 {
        struct cgroup *cgrp = seq_css(seq)->cgroup;
 
-       cgroup_print_ss_mask(seq, cgrp->child_subsys_mask);
+       cgroup_print_ss_mask(seq, cgrp->subtree_control);
        return 0;
 }
 
@@ -2608,7 +2616,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 
        for_each_subsys(ss, ssid) {
                if (enable & (1 << ssid)) {
-                       if (cgrp->child_subsys_mask & (1 << ssid)) {
+                       if (cgrp->subtree_control & (1 << ssid)) {
                                enable &= ~(1 << ssid);
                                continue;
                        }
@@ -2616,7 +2624,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                        /* 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)))) {
+                            !(cgroup_parent(cgrp)->subtree_control & (1 << ssid)))) {
                                ret = -ENOENT;
                                goto out_unlock;
                        }
@@ -2644,14 +2652,14 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                return restart_syscall();
                        }
                } else if (disable & (1 << ssid)) {
-                       if (!(cgrp->child_subsys_mask & (1 << ssid))) {
+                       if (!(cgrp->subtree_control & (1 << ssid))) {
                                disable &= ~(1 << ssid);
                                continue;
                        }
 
                        /* a child has it enabled? */
                        cgroup_for_each_live_child(child, cgrp) {
-                               if (child->child_subsys_mask & (1 << ssid)) {
+                               if (child->subtree_control & (1 << ssid)) {
                                        ret = -EBUSY;
                                        goto out_unlock;
                                }
@@ -2665,7 +2673,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
        }
 
        /*
-        * Except for the root, child_subsys_mask must be zero for a cgroup
+        * Except for the root, subtree_control must be zero for a cgroup
         * with tasks so that child cgroups don't compete against tasks.
         */
        if (enable && cgroup_parent(cgrp) && !list_empty(&cgrp->cset_links)) {
@@ -2673,8 +2681,9 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                goto out_unlock;
        }
 
-       cgrp->child_subsys_mask |= enable;
-       cgrp->child_subsys_mask &= ~disable;
+       cgrp->subtree_control |= enable;
+       cgrp->subtree_control &= ~disable;
+       cgroup_refresh_child_subsys_mask(cgrp);
 
        /* create new csses */
        for_each_subsys(ss, ssid) {
@@ -2713,8 +2722,9 @@ out_unlock:
        return ret ?: nbytes;
 
 err_undo_css:
-       cgrp->child_subsys_mask &= ~enable;
-       cgrp->child_subsys_mask |= disable;
+       cgrp->subtree_control &= ~enable;
+       cgrp->subtree_control |= disable;
+       cgroup_refresh_child_subsys_mask(cgrp);
 
        for_each_subsys(ss, ssid) {
                if (!(enable & (1 << ssid)))
@@ -4428,10 +4438,12 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 
        /*
         * On the default hierarchy, a child doesn't automatically inherit
-        * child_subsys_mask from the parent.  Each is configured manually.
+        * subtree_control from the parent.  Each is configured manually.
         */
-       if (!cgroup_on_dfl(cgrp))
-               cgrp->child_subsys_mask = parent->child_subsys_mask;
+       if (!cgroup_on_dfl(cgrp)) {
+               cgrp->subtree_control = parent->subtree_control;
+               cgroup_refresh_child_subsys_mask(cgrp);
+       }
 
        kernfs_activate(kn);