cgroup: explicitly track whether a cgroup_subsys_state is visible to userland

Currently, whether a css (cgroup_subsys_state) has its interface files
created is not tracked and assumed to change together with the owning
cgroup's lifecycle.  cgroup directory and interface creation is being
separated out from internal object creation to help refactoring and
eventually allow cgroups which are not visible through cgroupfs.

This patch adds CSS_VISIBLE to track whether a css has its interface
files created and perform management operations only when necessary
which helps decoupling interface file handling from internal object
lifecycle.  After this patch, all css interface file management
functions can be called regardless of the current state and will
achieve the expected result.

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

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 8fc3f04522890cb56fff22d29879c397107c9552..7593c1a467860ae686b6dc54f0cad702ceb9debb 100644 (file)
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -45,6 +45,7 @@ enum {
        CSS_NO_REF      = (1 << 0), /* no reference counting for this css */
        CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
        CSS_RELEASED    = (1 << 2), /* refcnt reached zero, released */
+       CSS_VISIBLE     = (1 << 3), /* css is visible to userland */
 };
 
 /* bits in struct cgroup flags field */

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4178e45becb45de4ac81191e432d536d3b196267..a9a53ca942f3bbcb9afd4e441564d02f98706161 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1421,6 +1421,11 @@ static void css_clear_dir(struct cgroup_subsys_state *css,
        struct cgroup *cgrp = cgrp_override ?: css->cgroup;
        struct cftype *cfts;
 
+       if (!(css->flags & CSS_VISIBLE))
+               return;
+
+       css->flags &= ~CSS_VISIBLE;
+
        list_for_each_entry(cfts, &css->ss->cfts, node)
                cgroup_addrm_files(css, cgrp, cfts, false);
 }
@@ -1439,6 +1444,9 @@ static int css_populate_dir(struct cgroup_subsys_state *css,
        struct cftype *cfts, *failed_cfts;
        int ret;
 
+       if (css->flags & CSS_VISIBLE)
+               return 0;
+
        if (!css->ss) {
                if (cgroup_on_dfl(cgrp))
                        cfts = cgroup_dfl_base_files;
@@ -1455,6 +1463,9 @@ static int css_populate_dir(struct cgroup_subsys_state *css,
                        goto err;
                }
        }
+
+       css->flags |= CSS_VISIBLE;
+
        return 0;
 err:
        list_for_each_entry(cfts, &css->ss->cfts, node) {
@@ -3403,7 +3414,7 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
        css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
                struct cgroup *cgrp = css->cgroup;
 
-               if (cgroup_is_dead(cgrp))
+               if (!(css->flags & CSS_VISIBLE))
                        continue;
 
                ret = cgroup_addrm_files(css, cgrp, cfts, is_add);