cgroup: increase maximum subsystem count from 16 to 32

The current cgroup subsystem limit of 16 is insufficient, as the number of
existing subsystems has already reached this limit. When adding a new
subsystem that is not yet in the mainline kernel, building with
`make allmodconfig` requires first bypassing the
`BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16)` restriction to allow compilation
to succeed. However, the kernel still fails to boot afterward.

This patch increases the maximum number of supported cgroup subsystems from
16 to 32, providing enough room for future subsystem additions.

Signed-off-by: Chen Ridong <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: JP Kobryn <[email protected]>
Acked-by: JP Kobryn <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: Chen Ridong

include/linux/cgroup-defs.h

@@ -535,10 +535,10 @@ struct cgroup {
 	 * one which may have more subsystems enabled.  Controller knobs
 	 * are made available iff it's enabled in ->subtree_control.
 	 */
-	u16 subtree_control;
-	u16 subtree_ss_mask;
-	u16 old_subtree_control;
-	u16 old_subtree_ss_mask;
+	u32 subtree_control;
+	u32 subtree_ss_mask;
+	u32 old_subtree_control;
+	u32 old_subtree_ss_mask;
 
 	/* Private pointers for each registered subsystem */
 	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];

include/trace/events/cgroup.h

@@ -16,7 +16,7 @@ DECLARE_EVENT_CLASS(cgroup_root,
 
 	TP_STRUCT__entry(
 		__field(	int,		root			)
-		__field(	u16,		ss_mask			)
+		__field(	u32,		ss_mask			)
 		__string(	name,		root->name		)
 	),
 

kernel/cgroup/cgroup-internal.h

@@ -52,7 +52,7 @@ struct cgroup_fs_context {
 	bool		cpuset_clone_children;
 	bool		none;			/* User explicitly requested empty subsystem */
 	bool		all_ss;			/* Seen 'all' option */
-	u16		subsys_mask;		/* Selected subsystems */
+	u32		subsys_mask;		/* Selected subsystems */
 	char		*name;			/* Hierarchy name */
 	char		*release_agent;		/* Path for release notifications */
 };
@@ -146,7 +146,7 @@ struct cgroup_mgctx {
 	struct cgroup_taskset	tset;
 
 	/* subsystems affected by migration */
-	u16			ss_mask;
+	u32			ss_mask;
 };
 
 #define CGROUP_TASKSET_INIT(tset)						\
@@ -235,8 +235,8 @@ int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
 void cgroup_favor_dynmods(struct cgroup_root *root, bool favor);
 void cgroup_free_root(struct cgroup_root *root);
 void init_cgroup_root(struct cgroup_fs_context *ctx);
-int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask);
-int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
+int cgroup_setup_root(struct cgroup_root *root, u32 ss_mask);
+int rebind_subsystems(struct cgroup_root *dst_root, u32 ss_mask);
 int cgroup_do_get_tree(struct fs_context *fc);
 
 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp);

kernel/cgroup/cgroup-v1.c

@@ -28,7 +28,7 @@
 #define CGROUP_PIDLIST_DESTROY_DELAY	HZ
 
 /* Controllers blocked by the commandline in v1 */
-static u16 cgroup_no_v1_mask;
+static u32 cgroup_no_v1_mask;
 
 /* disable named v1 mounts */
 static bool cgroup_no_v1_named;
@@ -1037,13 +1037,13 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
 static int check_cgroupfs_options(struct fs_context *fc)
 {
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
-	u16 mask = U16_MAX;
-	u16 enabled = 0;
+	u32 mask = U32_MAX;
+	u32 enabled = 0;
 	struct cgroup_subsys *ss;
 	int i;
 
 #ifdef CONFIG_CPUSETS
-	mask = ~((u16)1 << cpuset_cgrp_id);
+	mask = ~((u32)1 << cpuset_cgrp_id);
 #endif
 	for_each_subsys(ss, i)
 		if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i) &&
@@ -1095,7 +1095,7 @@ int cgroup1_reconfigure(struct fs_context *fc)
 	struct kernfs_root *kf_root = kernfs_root_from_sb(fc->root->d_sb);
 	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
 	int ret = 0;
-	u16 added_mask, removed_mask;
+	u32 added_mask, removed_mask;
 
 	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
 
@@ -1343,7 +1343,7 @@ static int __init cgroup_no_v1(char *str)
 			continue;
 
 		if (!strcmp(token, "all")) {
-			cgroup_no_v1_mask = U16_MAX;
+			cgroup_no_v1_mask = U32_MAX;
 			continue;
 		}
 

kernel/cgroup/cgroup.c

@@ -206,13 +206,13 @@ EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 bool cgrp_dfl_visible;
 
 /* some controllers are not supported in the default hierarchy */
-static u16 cgrp_dfl_inhibit_ss_mask;
+static u32 cgrp_dfl_inhibit_ss_mask;
 
 /* some controllers are implicitly enabled on the default hierarchy */
-static u16 cgrp_dfl_implicit_ss_mask;
+static u32 cgrp_dfl_implicit_ss_mask;
 
 /* some controllers can be threaded on the default hierarchy */
-static u16 cgrp_dfl_threaded_ss_mask;
+static u32 cgrp_dfl_threaded_ss_mask;
 
 /* The list of hierarchy roots */
 LIST_HEAD(cgroup_roots);
@@ -234,10 +234,10 @@ static u64 css_serial_nr_next = 1;
  * These bitmasks identify subsystems with specific features to avoid
  * having to do iterative checks repeatedly.
  */
-static u16 have_fork_callback __read_mostly;
-static u16 have_exit_callback __read_mostly;
-static u16 have_release_callback __read_mostly;
-static u16 have_canfork_callback __read_mostly;
+static u32 have_fork_callback __read_mostly;
+static u32 have_exit_callback __read_mostly;
+static u32 have_release_callback __read_mostly;
+static u32 have_canfork_callback __read_mostly;
 
 static bool have_favordynmods __ro_after_init = IS_ENABLED(CONFIG_CGROUP_FAVOR_DYNMODS);
 
@@ -475,13 +475,13 @@ static bool cgroup_is_valid_domain(struct cgroup *cgrp)
 }
 
 /* subsystems visibly enabled on a cgroup */
-static u16 cgroup_control(struct cgroup *cgrp)
+static u32 cgroup_control(struct cgroup *cgrp)
 {
 	struct cgroup *parent = cgroup_parent(cgrp);
-	u16 root_ss_mask = cgrp->root->subsys_mask;
+	u32 root_ss_mask = cgrp->root->subsys_mask;
 
 	if (parent) {
-		u16 ss_mask = parent->subtree_control;
+		u32 ss_mask = parent->subtree_control;
 
 		/* threaded cgroups can only have threaded controllers */
 		if (cgroup_is_threaded(cgrp))
@@ -496,12 +496,12 @@ static u16 cgroup_control(struct cgroup *cgrp)
 }
 
 /* subsystems enabled on a cgroup */
-static u16 cgroup_ss_mask(struct cgroup *cgrp)
+static u32 cgroup_ss_mask(struct cgroup *cgrp)
 {
 	struct cgroup *parent = cgroup_parent(cgrp);
 
 	if (parent) {
-		u16 ss_mask = parent->subtree_ss_mask;
+		u32 ss_mask = parent->subtree_ss_mask;
 
 		/* threaded cgroups can only have threaded controllers */
 		if (cgroup_is_threaded(cgrp))
@@ -1636,9 +1636,9 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
  * This function calculates which subsystems need to be enabled if
  * @subtree_control is to be applied while restricted to @this_ss_mask.
  */
-static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
+static u32 cgroup_calc_subtree_ss_mask(u32 subtree_control, u32 this_ss_mask)
 {
-	u16 cur_ss_mask = subtree_control;
+	u32 cur_ss_mask = subtree_control;
 	struct cgroup_subsys *ss;
 	int ssid;
 
@@ -1647,7 +1647,7 @@ static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
 	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
 
 	while (true) {
-		u16 new_ss_mask = cur_ss_mask;
+		u32 new_ss_mask = cur_ss_mask;
 
 		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
 			new_ss_mask |= ss->depends_on;
@@ -1851,12 +1851,12 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 	return ret;
 }
 
-int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
+int rebind_subsystems(struct cgroup_root *dst_root, u32 ss_mask)
 {
 	struct cgroup *dcgrp = &dst_root->cgrp;
 	struct cgroup_subsys *ss;
 	int ssid, ret;
-	u16 dfl_disable_ss_mask = 0;
+	u32 dfl_disable_ss_mask = 0;
 
 	lockdep_assert_held(&cgroup_mutex);
 
@@ -2152,7 +2152,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx)
 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
 }
 
-int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
+int cgroup_setup_root(struct cgroup_root *root, u32 ss_mask)
 {
 	LIST_HEAD(tmp_links);
 	struct cgroup *root_cgrp = &root->cgrp;
@@ -3134,7 +3134,7 @@ void cgroup_procs_write_finish(struct task_struct *task,
 	put_task_struct(task);
 }
 
-static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
+static void cgroup_print_ss_mask(struct seq_file *seq, u32 ss_mask)
 {
 	struct cgroup_subsys *ss;
 	bool printed = false;
@@ -3499,9 +3499,9 @@ static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
 	cgroup_apply_control_disable(cgrp);
 }
 
-static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
+static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u32 enable)
 {
-	u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
+	u32 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
 
 	/* if nothing is getting enabled, nothing to worry about */
 	if (!enable)
@@ -3544,7 +3544,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 					    char *buf, size_t nbytes,
 					    loff_t off)
 {
-	u16 enable = 0, disable = 0;
+	u32 enable = 0, disable = 0;
 	struct cgroup *cgrp, *child;
 	struct cgroup_subsys *ss;
 	char *tok;
@@ -6350,7 +6350,7 @@ int __init cgroup_init(void)
 	struct cgroup_subsys *ss;
 	int ssid;
 
-	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
+	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 32);
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_psi_files));
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));

kernel/cgroup/debug.c

@@ -230,7 +230,7 @@ static int cgroup_subsys_states_read(struct seq_file *seq, void *v)
 }
 
 static void cgroup_masks_read_one(struct seq_file *seq, const char *name,
-				  u16 mask)
+				  u32 mask)
 {
 	struct cgroup_subsys *ss;
 	int ssid;