From a2dd424750807f83632a2a70293961086fd8f870 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 19 Mar 2014 10:23:55 -0400 Subject: [PATCH] cgroup: make cgrp_dfl_root mountable cgrp_dfl_root will be used as the default unified hierarchy. This patch makes cgrp_dfl_root mountable by making the following changes. * cgroup_init_early() now initializes cgrp_dfl_root w/ CGRP_ROOT_SANE_BEHAVIOR. The default hierarchy is always sane. * parse_cgroupfs_options() and cgroup_mount() are updated such that cgrp_dfl_root is mounted if sane_behavior is specified w/o any subsystems. * rebind_subsystems() now populates the root directory of cgrp_dfl_root. Note that the function still guarantees success of rebinding subsystems to cgrp_dfl_root. If populating fails while rebinding to cgrp_dfl_root, it whines but ignores the error. * For backward compatibility, the default hierarchy shows up in /proc/$PID/cgroup only after it's explicitly mounted so that userland which doesn't make use of it doesn't see any change. * "current_css_set_cg_links" file of debug cgroup now treats the default hierarchy the same as other hierarchies. This is visible to userland. Given that it's for debug controller, this should be fine. * While at it, implement cgroup_on_dfl() which tests whether a give cgroup is on the default hierarchy or not. The above changes make cgrp_dfl_root mostly equivalent to other controllers but the actual unified hierarchy behaviors are not implemented yet. Let's plug child cgroup creation in cgrp_dfl_root from create_cgroup() for now. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- include/linux/cgroup.h | 10 +++++ kernel/cgroup.c | 94 +++++++++++++++++++++++++++--------------- 2 files changed, 71 insertions(+), 33 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 79993ac066c5..7e9fa505b7bb 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -250,6 +250,9 @@ enum { * * - "cgroup.clone_children" is removed. * + * - If mount is requested with sane_behavior but without any + * subsystem, the default unified hierarchy is mounted. + * * - cpuset: tasks will be kept in empty cpusets when hotplug happens * and take masks of ancestors with non-empty cpus/mems, instead of * being moved to an ancestor. @@ -468,6 +471,13 @@ struct cftype { #endif }; +extern struct cgroup_root cgrp_dfl_root; + +static inline bool cgroup_on_dfl(const struct cgroup *cgrp) +{ + return cgrp->root == &cgrp_dfl_root; +} + /* * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details. This * function can be called as long as @cgrp is accessible. diff --git a/kernel/cgroup.c b/kernel/cgroup.c index f5754910e80b..69b4939e9f6d 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -142,7 +142,13 @@ static const char *cgroup_subsys_name[] = { * unattached - it never has more than a single cgroup, and all tasks are * part of that cgroup. */ -static struct cgroup_root cgrp_dfl_root; +struct cgroup_root cgrp_dfl_root; + +/* + * The default hierarchy always exists but is hidden until mounted for the + * first time. This is for backward compatibility. + */ +static bool cgrp_dfl_root_visible; /* The list of hierarchy roots */ @@ -999,10 +1005,22 @@ static int rebind_subsystems(struct cgroup_root *dst_root, return -EBUSY; } - if (dst_root != &cgrp_dfl_root) { - ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask); - if (ret) + ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask); + if (ret) { + if (dst_root != &cgrp_dfl_root) return ret; + + /* + * Rebinding back to the default root is not allowed to + * fail. Using both default and non-default roots should + * be rare. Moving subsystems back and forth even more so. + * Just warn about it and continue. + */ + if (cgrp_dfl_root_visible) { + pr_warning("cgroup: failed to create files (%d) while rebinding 0x%lx to default root\n", + ret, ss_mask); + pr_warning("cgroup: you may retry by moving them to a different hierarchy and unbinding\n"); + } } /* @@ -1011,7 +1029,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root, */ mutex_unlock(&cgroup_mutex); for_each_subsys(ss, ssid) - if ((ss_mask & (1 << ssid)) && ss->root != &cgrp_dfl_root) + if (ss_mask & (1 << ssid)) cgroup_clear_dir(&ss->root->cgrp, 1 << ssid); mutex_lock(&cgroup_mutex); @@ -1039,8 +1057,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root, ss->bind(css); } - if (dst_root != &cgrp_dfl_root) - kernfs_activate(dst_root->cgrp.kn); + kernfs_activate(dst_root->cgrp.kn); return 0; } @@ -1190,16 +1207,6 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) return -ENOENT; } - /* - * If the 'all' option was specified select all the subsystems, - * otherwise if 'none', 'name=' and a subsystem name options - * were not specified, let's default to 'all' - */ - if (all_ss || (!one_ss && !opts->none && !opts->name)) - for_each_subsys(ss, i) - if (!ss->disabled) - set_bit(i, &opts->subsys_mask); - /* Consistency checks */ if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) { @@ -1211,6 +1218,23 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n"); return -EINVAL; } + } else { + /* + * If the 'all' option was specified select all the + * subsystems, otherwise if 'none', 'name=' and a subsystem + * name options were not specified, let's default to 'all' + */ + if (all_ss || (!one_ss && !opts->none && !opts->name)) + for_each_subsys(ss, i) + if (!ss->disabled) + set_bit(i, &opts->subsys_mask); + + /* + * We either have to specify by name or by subsystems. (So + * all empty hierarchies must have a name). + */ + if (!opts->subsys_mask && !opts->name) + return -EINVAL; } /* @@ -1226,13 +1250,6 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) if (opts->subsys_mask && opts->none) return -EINVAL; - /* - * We either have to specify by name or by subsystems. (So all - * empty hierarchies must have a name). - */ - if (!opts->subsys_mask && !opts->name) - return -EINVAL; - return 0; } @@ -1487,6 +1504,14 @@ retry: goto out_unlock; /* look for a matching existing root */ + if (!opts.subsys_mask && !opts.none && !opts.name) { + cgrp_dfl_root_visible = true; + root = &cgrp_dfl_root; + cgroup_get(&root->cgrp); + ret = 0; + goto out_unlock; + } + for_each_root(root) { bool name_match = false; @@ -3622,6 +3647,13 @@ static long cgroup_create(struct cgroup *parent, const char *name, struct cgroup_subsys *ss; struct kernfs_node *kn; + /* + * XXX: The default hierarchy isn't fully implemented yet. Block + * !root cgroup creation on it for now. + */ + if (root == &cgrp_dfl_root) + return -EINVAL; + /* allocate the cgroup and its ID, 0 is reserved for the root */ cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL); if (!cgrp) @@ -4061,7 +4093,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) */ int __init cgroup_init_early(void) { - static struct cgroup_sb_opts __initdata opts = { }; + static struct cgroup_sb_opts __initdata opts = + { .flags = CGRP_ROOT_SANE_BEHAVIOR }; struct cgroup_subsys *ss; int i; @@ -4198,7 +4231,7 @@ int proc_cgroup_show(struct seq_file *m, void *v) struct cgroup *cgrp; int ssid, count = 0; - if (root == &cgrp_dfl_root) + if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible) continue; seq_printf(m, "%d:", root->hierarchy_id); @@ -4631,15 +4664,10 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v) cset = rcu_dereference(current->cgroups); list_for_each_entry(link, &cset->cgrp_links, cgrp_link) { struct cgroup *c = link->cgrp; - const char *name = "?"; - - if (c != &cgrp_dfl_root.cgrp) { - cgroup_name(c, name_buf, NAME_MAX + 1); - name = name_buf; - } + cgroup_name(c, name_buf, NAME_MAX + 1); seq_printf(seq, "Root %d group %s\n", - c->root->hierarchy_id, name); + c->root->hierarchy_id, name_buf); } rcu_read_unlock(); up_read(&css_set_rwsem);