---

yaml
---
r: 187206
b: refs/heads/master
c: aae8aab
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d7b9fff711d5e8db8c844161c684017e556c38a0
+refs/heads/master: aae8aab40367036931608fdaf9e2dc568b516f19

trunk/include/linux/cgroup.h

@@ -40,13 +40,19 @@ extern int cgroupstats_build(struct cgroupstats *stats,
 
 extern const struct file_operations proc_cgroup_operations;
 
-/* Define the enumeration of all cgroup subsystems */
+/* Define the enumeration of all builtin cgroup subsystems */
 #define SUBSYS(_x) _x ## _subsys_id,
 enum cgroup_subsys_id {
 #include <linux/cgroup_subsys.h>
-	CGROUP_SUBSYS_COUNT
+	CGROUP_BUILTIN_SUBSYS_COUNT
 };
 #undef SUBSYS
+/*
+ * This define indicates the maximum number of subsystems that can be loaded
+ * at once. We limit to this many since cgroupfs_root has subsys_bits to keep
+ * track of all of them.
+ */
+#define CGROUP_SUBSYS_COUNT (BITS_PER_BYTE*sizeof(unsigned long))
 
 /* Per-subsystem/per-cgroup state maintained by the system. */
 struct cgroup_subsys_state {

trunk/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
@@ -884,14 +891,18 @@ 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)
 {
 	unsigned long added_bits, removed_bits;
 	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)) {