cgroup: restructure file creation / removal handling

The file creation / removal path has always been a bit icky and the
planned notification update requires css during file creation.
Restructure as follows.

* cgroup_addrm_files() now takes both @css and @cgrp and is only
  called directly by other file handling functions.

* cgroup_populate/clear_dir() are replaced with
  css_populate/clear_dir() taking @css and @cgrp_override.
  @cgrp_override is used only when files needs to be created on /
  removed from a cgroup which isn't attached to @css which happens
  during subsystem rebinds.  Subsystem loops are moved to the callers.

* cgroup_add_file() now takes both @css and @cgrp.  @css isn't used
  yet but will be used by the planned notification update.

This patch doens't cause any behavior changes.

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

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a4ff4965e53b44404226eccb9e95f150402a6c09..06c9d1aeea9d2d62adb344bdd19a664b86aa6c8a 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -221,7 +221,8 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
                      bool visible);
 static void css_release(struct percpu_ref *ref);
 static void kill_css(struct cgroup_subsys_state *css);
-static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+                             struct cgroup *cgrp, struct cftype cfts[],
                              bool is_add);
 
 /**
@@ -1313,53 +1314,57 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
 }
 
 /**
- * cgroup_clear_dir - remove subsys files in a cgroup directory
- * @cgrp: target cgroup
- * @subsys_mask: mask of the subsystem ids whose files should be removed
+ * css_clear_dir - remove subsys files in a cgroup directory
+ * @css: taget css
+ * @cgrp_override: specify if target cgroup is different from css->cgroup
  */
-static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
+static void css_clear_dir(struct cgroup_subsys_state *css,
+                         struct cgroup *cgrp_override)
 {
-       struct cgroup_subsys *ss;
-       int i;
+       struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+       struct cftype *cfts;
 
-       for_each_subsys(ss, i) {
-               struct cftype *cfts;
-
-               if (!(subsys_mask & (1 << i)))
-                       continue;
-               list_for_each_entry(cfts, &ss->cfts, node)
-                       cgroup_addrm_files(cgrp, cfts, false);
-       }
+       list_for_each_entry(cfts, &css->ss->cfts, node)
+               cgroup_addrm_files(css, cgrp, cfts, false);
 }
 
 /**
- * cgroup_populate_dir - create subsys files in a cgroup directory
- * @cgrp: target cgroup
- * @subsys_mask: mask of the subsystem ids whose files should be added
+ * css_populate_dir - create subsys files in a cgroup directory
+ * @css: target css
+ * @cgrp_overried: specify if target cgroup is different from css->cgroup
  *
  * On failure, no file is added.
  */
-static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
+static int css_populate_dir(struct cgroup_subsys_state *css,
+                           struct cgroup *cgrp_override)
 {
-       struct cgroup_subsys *ss;
-       int i, ret = 0;
+       struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+       struct cftype *cfts, *failed_cfts;
+       int ret;
 
-       /* process cftsets of each subsystem */
-       for_each_subsys(ss, i) {
-               struct cftype *cfts;
+       if (!css->ss) {
+               if (cgroup_on_dfl(cgrp))
+                       cfts = cgroup_dfl_base_files;
+               else
+                       cfts = cgroup_legacy_base_files;
 
-               if (!(subsys_mask & (1 << i)))
-                       continue;
+               return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
+       }
 
-               list_for_each_entry(cfts, &ss->cfts, node) {
-                       ret = cgroup_addrm_files(cgrp, cfts, true);
-                       if (ret < 0)
-                               goto err;
+       list_for_each_entry(cfts, &css->ss->cfts, node) {
+               ret = cgroup_addrm_files(css, cgrp, cfts, true);
+               if (ret < 0) {
+                       failed_cfts = cfts;
+                       goto err;
                }
        }
        return 0;
 err:
-       cgroup_clear_dir(cgrp, subsys_mask);
+       list_for_each_entry(cfts, &css->ss->cfts, node) {
+               if (cfts == failed_cfts)
+                       break;
+               cgroup_addrm_files(css, cgrp, cfts, false);
+       }
        return ret;
 }
 
@@ -1388,10 +1393,13 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
        if (dst_root == &cgrp_dfl_root)
                tmp_ss_mask &= ~cgrp_dfl_root_inhibit_ss_mask;
 
-       ret = cgroup_populate_dir(dcgrp, tmp_ss_mask);
-       if (ret) {
-               if (dst_root != &cgrp_dfl_root)
-                       return ret;
+       for_each_subsys_which(ss, ssid, &tmp_ss_mask) {
+               struct cgroup *scgrp = &ss->root->cgrp;
+               int tssid;
+
+               ret = css_populate_dir(cgroup_css(scgrp, ss), dcgrp);
+               if (!ret)
+                       continue;
 
                /*
                 * Rebinding back to the default root is not allowed to
@@ -1399,20 +1407,27 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
                 * be rare.  Moving subsystems back and forth even more so.
                 * Just warn about it and continue.
                 */
-               if (cgrp_dfl_root_visible) {
-                       pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
-                               ret, ss_mask);
-                       pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
+               if (dst_root == &cgrp_dfl_root) {
+                       if (cgrp_dfl_root_visible) {
+                               pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
+                                       ret, ss_mask);
+                               pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
+                       }
+                       continue;
                }
+
+               for_each_subsys_which(ss, tssid, &tmp_ss_mask) {
+                       if (tssid == ssid)
+                               break;
+                       css_clear_dir(cgroup_css(scgrp, ss), dcgrp);
+               }
+               return ret;
        }
 
        /*
         * Nothing can fail from this point on.  Remove files for the
         * removed subsystems and rebind each subsystem.
         */
-       for_each_subsys_which(ss, ssid, &ss_mask)
-               cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
-
        for_each_subsys_which(ss, ssid, &ss_mask) {
                struct cgroup_root *src_root = ss->root;
                struct cgroup *scgrp = &src_root->cgrp;
@@ -1421,6 +1436,8 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 
                WARN_ON(!css || cgroup_css(dcgrp, ss));
 
+               css_clear_dir(css, NULL);
+
                RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
                rcu_assign_pointer(dcgrp->subsys[ssid], css);
                ss->root = dst_root;
@@ -1791,7 +1808,6 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
 {
        LIST_HEAD(tmp_links);
        struct cgroup *root_cgrp = &root->cgrp;
-       struct cftype *base_files;
        struct css_set *cset;
        int i, ret;
 
@@ -1830,12 +1846,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
        }
        root_cgrp->kn = root->kf_root->kn;
 
-       if (root == &cgrp_dfl_root)
-               base_files = cgroup_dfl_base_files;
-       else
-               base_files = cgroup_legacy_base_files;
-
-       ret = cgroup_addrm_files(root_cgrp, base_files, true);
+       ret = css_populate_dir(&root_cgrp->self, NULL);
        if (ret)
                goto destroy_root;
 
@@ -2985,7 +2996,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                                ret = create_css(child, ss,
                                        cgrp->subtree_control & (1 << ssid));
                        else
-                               ret = cgroup_populate_dir(child, 1 << ssid);
+                               ret = css_populate_dir(cgroup_css(child, ss),
+                                                      NULL);
                        if (ret)
                                goto err_undo_css;
                }
@@ -3018,7 +3030,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
                        if (css_disable & (1 << ssid)) {
                                kill_css(css);
                        } else {
-                               cgroup_clear_dir(child, 1 << ssid);
+                               css_clear_dir(css, NULL);
                                if (ss->css_reset)
                                        ss->css_reset(css);
                        }
@@ -3066,7 +3078,7 @@ err_undo_css:
                        if (css_enable & (1 << ssid))
                                kill_css(css);
                        else
-                               cgroup_clear_dir(child, 1 << ssid);
+                               css_clear_dir(css, NULL);
                }
        }
        goto out_unlock;
@@ -3218,7 +3230,8 @@ static int cgroup_kn_set_ugid(struct kernfs_node *kn)
        return kernfs_setattr(kn, &iattr);
 }
 
-static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
+static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
+                          struct cftype *cft)
 {
        char name[CGROUP_FILE_NAME_MAX];
        struct kernfs_node *kn;
@@ -3249,14 +3262,16 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
 
 /**
  * cgroup_addrm_files - add or remove files to a cgroup directory
- * @cgrp: the target cgroup
+ * @css: the target css
+ * @cgrp: the target cgroup (usually css->cgroup)
  * @cfts: array of cftypes to be added
  * @is_add: whether to add or remove
  *
  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
  * For removals, this function never fails.
  */
-static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+                             struct cgroup *cgrp, struct cftype cfts[],
                              bool is_add)
 {
        struct cftype *cft, *cft_end = NULL;
@@ -3277,7 +3292,7 @@ restart:
                        continue;
 
                if (is_add) {
-                       ret = cgroup_add_file(cgrp, cft);
+                       ret = cgroup_add_file(css, cgrp, cft);
                        if (ret) {
                                pr_warn("%s: failed to add %s, err=%d\n",
                                        __func__, cft->name, ret);
@@ -3309,7 +3324,7 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
                if (cgroup_is_dead(cgrp))
                        continue;
 
-               ret = cgroup_addrm_files(cgrp, cfts, is_add);
+               ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
                if (ret)
                        break;
        }
@@ -4685,7 +4700,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
        css->id = err;
 
        if (visible) {
-               err = cgroup_populate_dir(cgrp, 1 << ss->id);
+               err = css_populate_dir(css, NULL);
                if (err)
                        goto err_free_id;
        }
@@ -4711,7 +4726,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 
 err_list_del:
        list_del_rcu(&css->sibling);
-       cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
+       css_clear_dir(css, NULL);
 err_free_id:
        cgroup_idr_remove(&ss->css_idr, css->id);
 err_free_percpu_ref:
@@ -4728,7 +4743,6 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
        struct cgroup_root *root;
        struct cgroup_subsys *ss;
        struct kernfs_node *kn;
-       struct cftype *base_files;
        int ssid, ret;
 
        /* Do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable.
@@ -4804,12 +4818,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
        if (ret)
                goto out_destroy;
 
-       if (cgroup_on_dfl(cgrp))
-               base_files = cgroup_dfl_base_files;
-       else
-               base_files = cgroup_legacy_base_files;
-
-       ret = cgroup_addrm_files(cgrp, base_files, true);
+       ret = css_populate_dir(&cgrp->self, NULL);
        if (ret)
                goto out_destroy;
 
@@ -4896,7 +4905,7 @@ static void kill_css(struct cgroup_subsys_state *css)
         * This must happen before css is disassociated with its cgroup.
         * See seq_css() for details.
         */
-       cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
+       css_clear_dir(css, NULL);
 
        /*
         * Killing would put the base ref, but we need to keep it alive