diff options
| -rw-r--r-- | include/linux/cgroup.h | 10 | ||||
| -rw-r--r-- | kernel/cgroup.c | 96 |
2 files changed, 88 insertions, 18 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 14160b5..28319a9 100644 --- a/include/linux/cgroup.h +++ b/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 { diff --git a/kernel/cgroup.c b/kernel/cgroup.c index cace83d..c92fb95 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)) { |
