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-rw-r--r--kernel/cgroup.c96
1 files changed, 80 insertions, 16 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cace83ddbcdc..c92fb9549358 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -57,10 +57,14 @@
static DEFINE_MUTEX(cgroup_mutex);
-/* Generate an array of cgroup subsystem pointers */
+/*
+ * Generate an array of cgroup subsystem pointers. At boot time, this is
+ * populated up to CGROUP_BUILTIN_SUBSYS_COUNT, and modular subsystems are
+ * registered after that. The mutable section of this array is protected by
+ * cgroup_mutex.
+ */
#define SUBSYS(_x) &_x ## _subsys,
-
-static struct cgroup_subsys *subsys[] = {
+static struct cgroup_subsys *subsys[CGROUP_SUBSYS_COUNT] = {
#include <linux/cgroup_subsys.h>
};
@@ -448,8 +452,11 @@ static struct css_set *find_existing_css_set(
struct hlist_node *node;
struct css_set *cg;
- /* Built the set of subsystem state objects that we want to
- * see in the new css_set */
+ /*
+ * Build the set of subsystem state objects that we want to see in the
+ * new css_set. while subsystems can change globally, the entries here
+ * won't change, so no need for locking.
+ */
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
if (root->subsys_bits & (1UL << i)) {
/* Subsystem is in this hierarchy. So we want
@@ -884,7 +891,9 @@ void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
css_put(css);
}
-
+/*
+ * Call with cgroup_mutex held.
+ */
static int rebind_subsystems(struct cgroupfs_root *root,
unsigned long final_bits)
{
@@ -892,6 +901,8 @@ static int rebind_subsystems(struct cgroupfs_root *root,
struct cgroup *cgrp = &root->top_cgroup;
int i;
+ BUG_ON(!mutex_is_locked(&cgroup_mutex));
+
removed_bits = root->actual_subsys_bits & ~final_bits;
added_bits = final_bits & ~root->actual_subsys_bits;
/* Check that any added subsystems are currently free */
@@ -900,6 +911,12 @@ static int rebind_subsystems(struct cgroupfs_root *root,
struct cgroup_subsys *ss = subsys[i];
if (!(bit & added_bits))
continue;
+ /*
+ * Nobody should tell us to do a subsys that doesn't exist:
+ * parse_cgroupfs_options should catch that case and refcounts
+ * ensure that subsystems won't disappear once selected.
+ */
+ BUG_ON(ss == NULL);
if (ss->root != &rootnode) {
/* Subsystem isn't free */
return -EBUSY;
@@ -919,6 +936,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
unsigned long bit = 1UL << i;
if (bit & added_bits) {
/* We're binding this subsystem to this hierarchy */
+ BUG_ON(ss == NULL);
BUG_ON(cgrp->subsys[i]);
BUG_ON(!dummytop->subsys[i]);
BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
@@ -932,6 +950,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
mutex_unlock(&ss->hierarchy_mutex);
} else if (bit & removed_bits) {
/* We're removing this subsystem */
+ BUG_ON(ss == NULL);
BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
mutex_lock(&ss->hierarchy_mutex);
@@ -944,6 +963,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
mutex_unlock(&ss->hierarchy_mutex);
} else if (bit & final_bits) {
/* Subsystem state should already exist */
+ BUG_ON(ss == NULL);
BUG_ON(!cgrp->subsys[i]);
} else {
/* Subsystem state shouldn't exist */
@@ -986,14 +1006,18 @@ struct cgroup_sb_opts {
};
-/* Convert a hierarchy specifier into a bitmask of subsystems and
- * flags. */
+/*
+ * Convert a hierarchy specifier into a bitmask of subsystems and flags. Call
+ * with cgroup_mutex held to protect the subsys[] array.
+ */
static int parse_cgroupfs_options(char *data,
struct cgroup_sb_opts *opts)
{
char *token, *o = data ?: "all";
unsigned long mask = (unsigned long)-1;
+ BUG_ON(!mutex_is_locked(&cgroup_mutex));
+
#ifdef CONFIG_CPUSETS
mask = ~(1UL << cpuset_subsys_id);
#endif
@@ -1009,6 +1033,8 @@ static int parse_cgroupfs_options(char *data,
opts->subsys_bits = 0;
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
+ if (ss == NULL)
+ continue;
if (!ss->disabled)
opts->subsys_bits |= 1ul << i;
}
@@ -1053,6 +1079,8 @@ static int parse_cgroupfs_options(char *data,
int i;
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
ss = subsys[i];
+ if (ss == NULL)
+ continue;
if (!strcmp(token, ss->name)) {
if (!ss->disabled)
set_bit(i, &opts->subsys_bits);
@@ -1306,7 +1334,9 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
struct cgroupfs_root *new_root;
/* First find the desired set of subsystems */
+ mutex_lock(&cgroup_mutex);
ret = parse_cgroupfs_options(data, &opts);
+ mutex_unlock(&cgroup_mutex);
if (ret)
goto out_err;
@@ -2918,8 +2948,14 @@ static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
/* We need to take each hierarchy_mutex in a consistent order */
int i;
+ /*
+ * No worry about a race with rebind_subsystems that might mess up the
+ * locking order, since both parties are under cgroup_mutex.
+ */
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
+ if (ss == NULL)
+ continue;
if (ss->root == root)
mutex_lock(&ss->hierarchy_mutex);
}
@@ -2931,6 +2967,8 @@ static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
+ if (ss == NULL)
+ continue;
if (ss->root == root)
mutex_unlock(&ss->hierarchy_mutex);
}
@@ -3054,11 +3092,16 @@ static int cgroup_has_css_refs(struct cgroup *cgrp)
* synchronization other than RCU, and the subsystem linked
* list isn't RCU-safe */
int i;
+ /*
+ * We won't need to lock the subsys array, because the subsystems
+ * we're concerned about aren't going anywhere since our cgroup root
+ * has a reference on them.
+ */
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
struct cgroup_subsys_state *css;
- /* Skip subsystems not in this hierarchy */
- if (ss->root != cgrp->root)
+ /* Skip subsystems not present or not in this hierarchy */
+ if (ss == NULL || ss->root != cgrp->root)
continue;
css = cgrp->subsys[ss->subsys_id];
/* When called from check_for_release() it's possible
@@ -3279,7 +3322,8 @@ int __init cgroup_init_early(void)
for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
INIT_HLIST_HEAD(&css_set_table[i]);
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /* at bootup time, we don't worry about modular subsystems */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
BUG_ON(!ss->name);
@@ -3314,7 +3358,8 @@ int __init cgroup_init(void)
if (err)
return err;
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /* at bootup time, we don't worry about modular subsystems */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
if (!ss->early_init)
cgroup_init_subsys(ss);
@@ -3423,9 +3468,16 @@ static int proc_cgroupstats_show(struct seq_file *m, void *v)
int i;
seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
+ /*
+ * ideally we don't want subsystems moving around while we do this.
+ * cgroup_mutex is also necessary to guarantee an atomic snapshot of
+ * subsys/hierarchy state.
+ */
mutex_lock(&cgroup_mutex);
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
+ if (ss == NULL)
+ continue;
seq_printf(m, "%s\t%d\t%d\t%d\n",
ss->name, ss->root->hierarchy_id,
ss->root->number_of_cgroups, !ss->disabled);
@@ -3483,7 +3535,12 @@ void cgroup_fork_callbacks(struct task_struct *child)
{
if (need_forkexit_callback) {
int i;
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /*
+ * forkexit callbacks are only supported for builtin
+ * subsystems, and the builtin section of the subsys array is
+ * immutable, so we don't need to lock the subsys array here.
+ */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
if (ss->fork)
ss->fork(ss, child);
@@ -3552,7 +3609,11 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
struct css_set *cg;
if (run_callbacks && need_forkexit_callback) {
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /*
+ * modular subsystems can't use callbacks, so no need to lock
+ * the subsys array
+ */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
if (ss->exit)
ss->exit(ss, tsk);
@@ -3844,8 +3905,11 @@ static int __init cgroup_disable(char *str)
while ((token = strsep(&str, ",")) != NULL) {
if (!*token)
continue;
-
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ /*
+ * cgroup_disable, being at boot time, can't know about module
+ * subsystems, so we don't worry about them.
+ */
+ for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
if (!strcmp(token, ss->name)) {
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.