cgroup: reimplement rebind_subsystems() using cgroup_apply_control() and friends
rebind_subsystem() open codes quite a bit of css and interface file
manipulations. It tries to be fail-safe but doesn't quite achieve it.
It can be greatly simplified by using the new css management helpers.
This patch reimplements rebind_subsytsems() using
cgroup_apply_control() and friends.
* The half-baked rollback on file creation failure is dropped. It is
an extremely cold path, failure isn't critical, and, aside from
kernel bugs, the only reason it can fail is memory allocation
failure which pretty much doesn't happen for small allocations.
* As cgroup_apply_control_disable() is now used to clean up root
cgroup on rebind, make sure that it doesn't end up killing root
csses.
* All callers of rebind_subsystems() are updated to use
cgroup_lock_and_drain_offline() as the apply_control functions
require drained subtree.
* This leaves cgroup_refresh_subtree_ss_mask() without any user.
Removed.
* css_populate_dir() and css_clear_dir() no longer needs
@cgrp_override parameter. Dropped.
* While at it, add WARN_ON() to rebind_subsystem() calls which are
expected to always succeed just in case.
While the rules visible to userland aren't changed, this
reimplementation not only simplifies rebind_subsystems() but also
allows it to disable and enable csses recursively. This can be used
to implement more flexible rebinding.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ee6951b..98e644b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -221,6 +221,8 @@
static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
+static int cgroup_apply_control(struct cgroup *cgrp);
+static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
static void css_task_iter_advance(struct css_task_iter *it);
static int cgroup_destroy_locked(struct cgroup *cgrp);
static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
@@ -1160,13 +1162,13 @@
struct cgroup *cgrp = &root->cgrp;
struct cgrp_cset_link *link, *tmp_link;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
BUG_ON(atomic_read(&root->nr_cgrps));
BUG_ON(!list_empty(&cgrp->self.children));
/* Rebind all subsystems back to the default hierarchy */
- rebind_subsystems(&cgrp_dfl_root, root->subsys_mask);
+ WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
/*
* Release all the links from cset_links to this hierarchy's
@@ -1352,19 +1354,6 @@
}
/**
- * cgroup_refresh_subtree_ss_mask - update subtree_ss_mask
- * @cgrp: the target cgroup
- *
- * Update @cgrp->subtree_ss_mask according to the current
- * @cgrp->subtree_control using cgroup_calc_subtree_ss_mask().
- */
-static void cgroup_refresh_subtree_ss_mask(struct cgroup *cgrp)
-{
- cgrp->subtree_ss_mask =
- cgroup_calc_subtree_ss_mask(cgrp, cgrp->subtree_control);
-}
-
-/**
* cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
* @kn: the kernfs_node being serviced
*
@@ -1459,12 +1448,10 @@
/**
* 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 css_clear_dir(struct cgroup_subsys_state *css,
- struct cgroup *cgrp_override)
+static void css_clear_dir(struct cgroup_subsys_state *css)
{
- struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+ struct cgroup *cgrp = css->cgroup;
struct cftype *cfts;
if (!(css->flags & CSS_VISIBLE))
@@ -1479,14 +1466,12 @@
/**
* 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 css_populate_dir(struct cgroup_subsys_state *css,
- struct cgroup *cgrp_override)
+static int css_populate_dir(struct cgroup_subsys_state *css)
{
- struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+ struct cgroup *cgrp = css->cgroup;
struct cftype *cfts, *failed_cfts;
int ret;
@@ -1526,7 +1511,6 @@
{
struct cgroup *dcgrp = &dst_root->cgrp;
struct cgroup_subsys *ss;
- u16 tmp_ss_mask;
int ssid, i, ret;
lockdep_assert_held(&cgroup_mutex);
@@ -1541,46 +1525,6 @@
return -EBUSY;
} while_each_subsys_mask();
- /* skip creating root files on dfl_root for inhibited subsystems */
- tmp_ss_mask = ss_mask;
- if (dst_root == &cgrp_dfl_root)
- tmp_ss_mask &= ~cgrp_dfl_inhibit_ss_mask;
-
- do_each_subsys_mask(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
- * 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 (dst_root == &cgrp_dfl_root) {
- if (cgrp_dfl_visible) {
- pr_warn("failed to create files (%d) while rebinding 0x%x to default root\n",
- ret, ss_mask);
- pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
- }
- continue;
- }
-
- do_each_subsys_mask(ss, tssid, tmp_ss_mask) {
- if (tssid == ssid)
- break;
- css_clear_dir(cgroup_css(scgrp, ss), dcgrp);
- } while_each_subsys_mask();
- return ret;
- } while_each_subsys_mask();
-
- /*
- * Nothing can fail from this point on. Remove files for the
- * removed subsystems and rebind each subsystem.
- */
do_each_subsys_mask(ss, ssid, ss_mask) {
struct cgroup_root *src_root = ss->root;
struct cgroup *scgrp = &src_root->cgrp;
@@ -1589,8 +1533,12 @@
WARN_ON(!css || cgroup_css(dcgrp, ss));
- css_clear_dir(css, NULL);
+ /* disable from the source */
+ src_root->subsys_mask &= ~(1 << ssid);
+ WARN_ON(cgroup_apply_control(scgrp));
+ cgroup_finalize_control(scgrp, 0);
+ /* rebind */
RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
rcu_assign_pointer(dcgrp->subsys[ssid], css);
ss->root = dst_root;
@@ -1602,20 +1550,20 @@
&dcgrp->e_csets[ss->id]);
spin_unlock_bh(&css_set_lock);
- src_root->subsys_mask &= ~(1 << ssid);
- scgrp->subtree_control &= ~(1 << ssid);
- cgroup_refresh_subtree_ss_mask(scgrp);
-
/* default hierarchy doesn't enable controllers by default */
dst_root->subsys_mask |= 1 << ssid;
if (dst_root == &cgrp_dfl_root) {
static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
} else {
dcgrp->subtree_control |= 1 << ssid;
- cgroup_refresh_subtree_ss_mask(dcgrp);
static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
}
+ ret = cgroup_apply_control(dcgrp);
+ if (ret)
+ pr_warn("partial failure to rebind %s controller (err=%d)\n",
+ ss->name, ret);
+
if (ss->bind)
ss->bind(css);
} while_each_subsys_mask();
@@ -1807,7 +1755,7 @@
return -EINVAL;
}
- mutex_lock(&cgroup_mutex);
+ cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
/* See what subsystems are wanted */
ret = parse_cgroupfs_options(data, &opts);
@@ -1840,7 +1788,7 @@
if (ret)
goto out_unlock;
- rebind_subsystems(&cgrp_dfl_root, removed_mask);
+ WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
if (opts.release_agent) {
spin_lock(&release_agent_path_lock);
@@ -1991,7 +1939,7 @@
}
root_cgrp->kn = root->kf_root->kn;
- ret = css_populate_dir(&root_cgrp->self, NULL);
+ ret = css_populate_dir(&root_cgrp->self);
if (ret)
goto destroy_root;
@@ -2070,7 +2018,7 @@
goto out_mount;
}
- mutex_lock(&cgroup_mutex);
+ cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
/* First find the desired set of subsystems */
ret = parse_cgroupfs_options(data, &opts);
@@ -3123,7 +3071,7 @@
}
if (cgroup_control(dsct) & (1 << ss->id)) {
- ret = css_populate_dir(css, NULL);
+ ret = css_populate_dir(css);
if (ret)
return ret;
}
@@ -3162,10 +3110,11 @@
if (!css)
continue;
- if (!(cgroup_ss_mask(dsct) & (1 << ss->id))) {
+ if (css->parent &&
+ !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
kill_css(css);
} else if (!(cgroup_control(dsct) & (1 << ss->id))) {
- css_clear_dir(css, NULL);
+ css_clear_dir(css);
if (ss->css_reset)
ss->css_reset(css);
}
@@ -5159,7 +5108,7 @@
if (ret)
goto out_destroy;
- ret = css_populate_dir(&cgrp->self, NULL);
+ ret = css_populate_dir(&cgrp->self);
if (ret)
goto out_destroy;
@@ -5231,7 +5180,7 @@
* This must happen before css is disassociated with its cgroup.
* See seq_css() for details.
*/
- css_clear_dir(css, NULL);
+ css_clear_dir(css);
/*
* Killing would put the base ref, but we need to keep it alive