Controllers set to bypass mode in the parent's "cgroup.subtree_control"
can now be optionally enabled by writing the controller name with the
'+' prefix to "cgroup.controllers". Using the '#' prefix will reset it
back to the bypass state.
This capability increases the flexibility each controller has in
shaping the effective cgroup hierarchy to best suit its need.
Signed-off-by: Waiman Long <long...@redhat.com>
---
Documentation/cgroup-v2.txt | 23 +++++++++-
include/linux/cgroup-defs.h | 7 +++
kernel/cgroup/cgroup.c | 109 ++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 134 insertions(+), 5 deletions(-)
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index f17a74b..efb69c4 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -395,6 +395,18 @@ prefixed controller interface files from C and D. This
means that the
controller interface files - anything which doesn't start with
"cgroup." are owned by the parent rather than the cgroup itself.
+Once a controller is put into bypass mode in "cgroup.subtree_control",
+the cgroup's children can optionally enable this controller by writing
+the controller name with the '+ prefix into "cgroup.controllers".
+In this case, the controller interface files are considered to be
+owned by the child cgroup itself, not by its parent. Therefore,
+setting the bypass mode in "cgroup.subtree_control" means delegating
+the authority of enabling or disabling the controller interface files
+to its children. Writing the controller name with the '#' prefix into
+"cgroup.controllers" resets the state back to bypass mode. The state
+of a controller cannot be changed if it is enabled or bypassed in its
+"cgroup.subtree_control".
+
Cgroup Hierarchy
~~~~~~~~~~~~~~~~
@@ -859,11 +871,18 @@ All cgroup core files are prefixed with "cgroup."
should be granted along with the containing directory.
cgroup.controllers
- A read-only space separated values file which exists on all
+ A read-write space separated values file which exists on all
cgroups.
It shows space separated list of all controllers available to
- the cgroup. The controllers are not ordered.
+ the cgroup. Controller names with '#' prefix are in bypass
+ mode. The controllers are not ordered.
+
+ When a controller is set into bypass mode in its parent's
+ "cgroup.subtree_control", its name prefixed with '+' or '#'
+ can be written to enable it or reset it back to bypass mode
+ respectively. Controllers not in bypass mode are not allowed
+ to be written.
cgroup.subtree_control
A read-write space separated values file which exists on all
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 3cac6d0..25c2ac8 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -308,6 +308,13 @@ struct cgroup {
u16 old_subtree_ss_mask;
u16 old_subtree_bypass;
+ /*
+ * The bitmask of subsystems that are set in its parent's
+ * ->subtree_bypass and explictly enabled in this cgroup.
+ */
+ u16 enable_ss_mask;
+ u16 old_enable_ss_mask;
+
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 1e7feae..358d8b3 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -420,7 +420,7 @@ static u16 cgroup_control(struct cgroup *cgrp, bool
show_bypass)
u16 root_ss_mask = cgrp->root->subsys_mask;
if (parent) {
- u16 ss_mask = parent->subtree_control;
+ u16 ss_mask = parent->subtree_control|cgrp->enable_ss_mask;
if (show_bypass)
ss_mask |= parent->subtree_bypass;
@@ -443,7 +443,7 @@ static u16 cgroup_ss_mask(struct cgroup *cgrp, bool
show_bypass)
struct cgroup *parent = cgroup_parent(cgrp);
if (parent) {
- u16 ss_mask = parent->subtree_ss_mask;
+ u16 ss_mask = parent->subtree_ss_mask|cgrp->enable_ss_mask;
if (show_bypass)
@@ -2811,6 +2811,7 @@ static void cgroup_save_control(struct cgroup *cgrp)
dsct->old_subtree_control = dsct->subtree_control;
dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
dsct->old_subtree_bypass = dsct->subtree_bypass;
+ dsct->old_enable_ss_mask = dsct->enable_ss_mask;
}
}
@@ -2854,6 +2855,7 @@ static void cgroup_restore_control(struct cgroup *cgrp)
dsct->subtree_control = dsct->old_subtree_control;
dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
dsct->subtree_bypass = dsct->old_subtree_bypass;
+ dsct->enable_ss_mask = dsct->old_enable_ss_mask;
}
}
@@ -3124,7 +3126,8 @@ static ssize_t cgroup_subtree_control_write(struct
kernfs_open_file *of,
cgroup_for_each_live_child(child, cgrp)
- child_enable |= child->subtree_control|child->subtree_bypass;
+ child_enable |= child->subtree_control|child->subtree_bypass|
+ child->enable_ss_mask;
/*
* Cannot change the state of a controller if enabled in children.
@@ -3157,6 +3160,105 @@ static ssize_t cgroup_subtree_control_write(struct
kernfs_open_file *of,
return ret ?: nbytes;
}
+/*
+ * Change bypass status of controllers for a cgroup in the default hierarchy.
+ */
+static ssize_t cgroup_controllers_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes,
+ loff_t off)
+{
+ u16 enable = 0, bypass = 0;
+ struct cgroup *cgrp, *parent;
+ struct cgroup_subsys *ss;
+ char *tok;
+ int ssid, ret;
+
+ /*
+ * Parse input - space separated list of subsystem names prefixed
+ * with either + or #.
+ */
+ buf = strstrip(buf);
+ while ((tok = strsep(&buf, " "))) {
+ if (tok[0] == '\0')
+ continue;
+ do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
+ if (!cgroup_ssid_enabled(ssid) ||
+ strcmp(tok + 1, ss->name))
+ continue;
+
+ if (*tok == '+') {
+ enable |= 1 << ssid;
+ bypass &= ~(1 << ssid);
+ } else if (*tok == '#') {
+ bypass |= 1 << ssid;
+ enable &= ~(1 << ssid);
+ } else {
+ return -EINVAL;
+ }
+ break;
+ } while_each_subsys_mask();
+ if (ssid == CGROUP_SUBSYS_COUNT)
+ return -EINVAL;
+ }
+
+ cgrp = cgroup_kn_lock_live(of->kn, true);
+ if (!cgrp)
+ return -ENODEV;
+
+ /*
+ * Write to root cgroup's controllers file is not allowed.
+ */
+ parent = cgroup_parent(cgrp);
+ if (!parent) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ /*
+ * Only controllers set into bypass mode in the parent cgroup
+ * can be specified here.
+ */
+ if (~parent->subtree_bypass & (enable|bypass)) {
+ ret = -ENOENT;
+ goto out_unlock;
+ }
+
+ /*
+ * Mask off irrelevant bits.
+ */
+ enable &= ~cgrp->enable_ss_mask;
+ bypass &= cgrp->enable_ss_mask;
+
+ if (!(enable|bypass)) {
+ ret = 0;
+ goto out_unlock;
+ }
+
+ /*
+ * We cannot change the bypass state of a controller that is enabled
+ * in subtree_control.
+ */
+ if ((cgrp->subtree_control|cgrp->subtree_bypass) & (enable|bypass)) {
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+
+ /* Save and update control masks and prepare csses */
+ cgroup_save_control(cgrp);
+
+ cgrp->enable_ss_mask |= enable;
+ cgrp->enable_ss_mask &= ~bypass;
+
+ ret = cgroup_apply_control(cgrp);
+ cgroup_finalize_control(cgrp, ret);
+ kernfs_activate(cgrp->kn);
+ ret = 0;
+
+out_unlock:
+ cgroup_kn_unlock(of->kn);
+ return ret ?: nbytes;
+}
+
static int cgroup_enable_threaded(struct cgroup *cgrp)
{
struct cgroup *parent = cgroup_parent(cgrp);
@@ -4322,6 +4424,7 @@ static ssize_t cgroup_threads_write(struct
kernfs_open_file *of,
{
.name = "cgroup.controllers",
.seq_show = cgroup_controllers_show,
+ .write = cgroup_controllers_write,
},
{
.name = "cgroup.subtree_control",
--
1.8.3.1
