diff options
Diffstat (limited to 'kernel/cgroup_freezer.c')
| -rw-r--r-- | kernel/cgroup_freezer.c | 514 |
1 files changed, 309 insertions, 205 deletions
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index b1724ce98981..75dda1ea5026 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -22,24 +22,33 @@ #include <linux/freezer.h> #include <linux/seq_file.h> -enum freezer_state { - CGROUP_THAWED = 0, - CGROUP_FREEZING, - CGROUP_FROZEN, +/* + * A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is + * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared + * for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING + * for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of + * its ancestors has FREEZING_SELF set. + */ +enum freezer_state_flags { + CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */ + CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */ + CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */ + CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */ + + /* mask for all FREEZING flags */ + CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT, }; struct freezer { - struct cgroup_subsys_state css; - enum freezer_state state; - spinlock_t lock; /* protects _writes_ to state */ + struct cgroup_subsys_state css; + unsigned int state; + spinlock_t lock; }; -static inline struct freezer *cgroup_freezer( - struct cgroup *cgroup) +static inline struct freezer *cgroup_freezer(struct cgroup *cgroup) { - return container_of( - cgroup_subsys_state(cgroup, freezer_subsys_id), - struct freezer, css); + return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id), + struct freezer, css); } static inline struct freezer *task_freezer(struct task_struct *task) @@ -48,14 +57,21 @@ static inline struct freezer *task_freezer(struct task_struct *task) struct freezer, css); } +static struct freezer *parent_freezer(struct freezer *freezer) +{ + struct cgroup *pcg = freezer->css.cgroup->parent; + + if (pcg) + return cgroup_freezer(pcg); + return NULL; +} + bool cgroup_freezing(struct task_struct *task) { - enum freezer_state state; bool ret; rcu_read_lock(); - state = task_freezer(task)->state; - ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN; + ret = task_freezer(task)->state & CGROUP_FREEZING; rcu_read_unlock(); return ret; @@ -65,70 +81,18 @@ bool cgroup_freezing(struct task_struct *task) * cgroups_write_string() limits the size of freezer state strings to * CGROUP_LOCAL_BUFFER_SIZE */ -static const char *freezer_state_strs[] = { - "THAWED", - "FREEZING", - "FROZEN", +static const char *freezer_state_strs(unsigned int state) +{ + if (state & CGROUP_FROZEN) + return "FROZEN"; + if (state & CGROUP_FREEZING) + return "FREEZING"; + return "THAWED"; }; -/* - * State diagram - * Transitions are caused by userspace writes to the freezer.state file. - * The values in parenthesis are state labels. The rest are edge labels. - * - * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) - * ^ ^ | | - * | \_______THAWED_______/ | - * \__________________________THAWED____________/ - */ - struct cgroup_subsys freezer_subsys; -/* Locks taken and their ordering - * ------------------------------ - * cgroup_mutex (AKA cgroup_lock) - * freezer->lock - * css_set_lock - * task->alloc_lock (AKA task_lock) - * task->sighand->siglock - * - * cgroup code forces css_set_lock to be taken before task->alloc_lock - * - * freezer_create(), freezer_destroy(): - * cgroup_mutex [ by cgroup core ] - * - * freezer_can_attach(): - * cgroup_mutex (held by caller of can_attach) - * - * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): - * freezer->lock - * sighand->siglock (if the cgroup is freezing) - * - * freezer_read(): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * - * freezer_write() (freeze): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * sighand->siglock (fake signal delivery inside freeze_task()) - * - * freezer_write() (unfreeze): - * cgroup_mutex - * freezer->lock - * write_lock css_set_lock (cgroup iterator start) - * task->alloc_lock - * read_lock css_set_lock (cgroup iterator start) - * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator()) - * sighand->siglock - */ -static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup) +static struct cgroup_subsys_state *freezer_css_alloc(struct cgroup *cgroup) { struct freezer *freezer; @@ -137,160 +101,244 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup) return ERR_PTR(-ENOMEM); spin_lock_init(&freezer->lock); - freezer->state = CGROUP_THAWED; return &freezer->css; } -static void freezer_destroy(struct cgroup *cgroup) +/** + * freezer_css_online - commit creation of a freezer cgroup + * @cgroup: cgroup being created + * + * We're committing to creation of @cgroup. Mark it online and inherit + * parent's freezing state while holding both parent's and our + * freezer->lock. + */ +static int freezer_css_online(struct cgroup *cgroup) +{ + struct freezer *freezer = cgroup_freezer(cgroup); + struct freezer *parent = parent_freezer(freezer); + + /* + * The following double locking and freezing state inheritance + * guarantee that @cgroup can never escape ancestors' freezing + * states. See cgroup_for_each_descendant_pre() for details. + */ + if (parent) + spin_lock_irq(&parent->lock); + spin_lock_nested(&freezer->lock, SINGLE_DEPTH_NESTING); + + freezer->state |= CGROUP_FREEZER_ONLINE; + + if (parent && (parent->state & CGROUP_FREEZING)) { + freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN; + atomic_inc(&system_freezing_cnt); + } + + spin_unlock(&freezer->lock); + if (parent) + spin_unlock_irq(&parent->lock); + + return 0; +} + +/** + * freezer_css_offline - initiate destruction of @cgroup + * @cgroup: cgroup being destroyed + * + * @cgroup is going away. Mark it dead and decrement system_freezing_count + * if it was holding one. + */ +static void freezer_css_offline(struct cgroup *cgroup) { struct freezer *freezer = cgroup_freezer(cgroup); - if (freezer->state != CGROUP_THAWED) + spin_lock_irq(&freezer->lock); + + if (freezer->state & CGROUP_FREEZING) atomic_dec(&system_freezing_cnt); - kfree(freezer); + + freezer->state = 0; + + spin_unlock_irq(&freezer->lock); } -/* task is frozen or will freeze immediately when next it gets woken */ -static bool is_task_frozen_enough(struct task_struct *task) +static void freezer_css_free(struct cgroup *cgroup) { - return frozen(task) || - (task_is_stopped_or_traced(task) && freezing(task)); + kfree(cgroup_freezer(cgroup)); } /* - * The call to cgroup_lock() in the freezer.state write method prevents - * a write to that file racing against an attach, and hence the - * can_attach() result will remain valid until the attach completes. + * Tasks can be migrated into a different freezer anytime regardless of its + * current state. freezer_attach() is responsible for making new tasks + * conform to the current state. + * + * Freezer state changes and task migration are synchronized via + * @freezer->lock. freezer_attach() makes the new tasks conform to the + * current state and all following state changes can see the new tasks. */ -static int freezer_can_attach(struct cgroup *new_cgroup, - struct cgroup_taskset *tset) +static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset) { - struct freezer *freezer; + struct freezer *freezer = cgroup_freezer(new_cgrp); struct task_struct *task; + bool clear_frozen = false; + + spin_lock_irq(&freezer->lock); /* - * Anything frozen can't move or be moved to/from. + * Make the new tasks conform to the current state of @new_cgrp. + * For simplicity, when migrating any task to a FROZEN cgroup, we + * revert it to FREEZING and let update_if_frozen() determine the + * correct state later. + * + * Tasks in @tset are on @new_cgrp but may not conform to its + * current state before executing the following - !frozen tasks may + * be visible in a FROZEN cgroup and frozen tasks in a THAWED one. */ - cgroup_taskset_for_each(task, new_cgroup, tset) - if (cgroup_freezing(task)) - return -EBUSY; + cgroup_taskset_for_each(task, new_cgrp, tset) { + if (!(freezer->state & CGROUP_FREEZING)) { + __thaw_task(task); + } else { + freeze_task(task); + freezer->state &= ~CGROUP_FROZEN; + clear_frozen = true; + } + } - freezer = cgroup_freezer(new_cgroup); - if (freezer->state != CGROUP_THAWED) - return -EBUSY; + spin_unlock_irq(&freezer->lock); - return 0; + /* + * Propagate FROZEN clearing upwards. We may race with + * update_if_frozen(), but as long as both work bottom-up, either + * update_if_frozen() sees child's FROZEN cleared or we clear the + * parent's FROZEN later. No parent w/ !FROZEN children can be + * left FROZEN. + */ + while (clear_frozen && (freezer = parent_freezer(freezer))) { + spin_lock_irq(&freezer->lock); + freezer->state &= ~CGROUP_FROZEN; + clear_frozen = freezer->state & CGROUP_FREEZING; + spin_unlock_irq(&freezer->lock); + } } static void freezer_fork(struct task_struct *task) { struct freezer *freezer; - /* - * No lock is needed, since the task isn't on tasklist yet, - * so it can't be moved to another cgroup, which means the - * freezer won't be removed and will be valid during this - * function call. Nevertheless, apply RCU read-side critical - * section to suppress RCU lockdep false positives. - */ rcu_read_lock(); freezer = task_freezer(task); - rcu_read_unlock(); /* * The root cgroup is non-freezable, so we can skip the * following check. */ if (!freezer->css.cgroup->parent) - return; + goto out; spin_lock_irq(&freezer->lock); - BUG_ON(freezer->state == CGROUP_FROZEN); - - /* Locking avoids race with FREEZING -> THAWED transitions. */ - if (freezer->state == CGROUP_FREEZING) + if (freezer->state & CGROUP_FREEZING) freeze_task(task); spin_unlock_irq(&freezer->lock); +out: + rcu_read_unlock(); } -/* - * caller must hold freezer->lock +/** + * update_if_frozen - update whether a cgroup finished freezing + * @cgroup: cgroup of interest + * + * Once FREEZING is initiated, transition to FROZEN is lazily updated by + * calling this function. If the current state is FREEZING but not FROZEN, + * this function checks whether all tasks of this cgroup and the descendant + * cgroups finished freezing and, if so, sets FROZEN. + * + * The caller is responsible for grabbing RCU read lock and calling + * update_if_frozen() on all descendants prior to invoking this function. + * + * Task states and freezer state might disagree while tasks are being + * migrated into or out of @cgroup, so we can't verify task states against + * @freezer state here. See freezer_attach() for details. */ -static void update_if_frozen(struct cgroup *cgroup, - struct freezer *freezer) +static void update_if_frozen(struct cgroup *cgroup) { + struct freezer *freezer = cgroup_freezer(cgroup); + struct cgroup *pos; struct cgroup_iter it; struct task_struct *task; - unsigned int nfrozen = 0, ntotal = 0; - enum freezer_state old_state = freezer->state; - cgroup_iter_start(cgroup, &it); - while ((task = cgroup_iter_next(cgroup, &it))) { - ntotal++; - if (freezing(task) && is_task_frozen_enough(task)) - nfrozen++; + WARN_ON_ONCE(!rcu_read_lock_held()); + + spin_lock_irq(&freezer->lock); + + if (!(freezer->state & CGROUP_FREEZING) || + (freezer->state & CGROUP_FROZEN)) + goto out_unlock; + + /* are all (live) children frozen? */ + cgroup_for_each_child(pos, cgroup) { + struct freezer *child = cgroup_freezer(pos); + + if ((child->state & CGROUP_FREEZER_ONLINE) && + !(child->state & CGROUP_FROZEN)) + goto out_unlock; } - if (old_state == CGROUP_THAWED) { - BUG_ON(nfrozen > 0); - } else if (old_state == CGROUP_FREEZING) { - if (nfrozen == ntotal) - freezer->state = CGROUP_FROZEN; - } else { /* old_state == CGROUP_FROZEN */ - BUG_ON(nfrozen != ntotal); + /* are all tasks frozen? */ + cgroup_iter_start(cgroup, &it); + + while ((task = cgroup_iter_next(cgroup, &it))) { + if (freezing(task)) { + /* + * freezer_should_skip() indicates that the task + * should be skipped when determining freezing + * completion. Consider it frozen in addition to + * the usual frozen condition. + */ + if (!frozen(task) && !freezer_should_skip(task)) + goto out_iter_end; + } } + freezer->state |= CGROUP_FROZEN; +out_iter_end: cgroup_iter_end(cgroup, &it); +out_unlock: + spin_unlock_irq(&freezer->lock); } static int freezer_read(struct cgroup *cgroup, struct cftype *cft, struct seq_file *m) { - struct freezer *freezer; - enum freezer_state state; + struct cgroup *pos; - if (!cgroup_lock_live_group(cgroup)) - return -ENODEV; + rcu_read_lock(); - freezer = cgroup_freezer(cgroup); - spin_lock_irq(&freezer->lock); - state = freezer->state; - if (state == CGROUP_FREEZING) { - /* We change from FREEZING to FROZEN lazily if the cgroup was - * only partially frozen when we exitted write. */ - update_if_frozen(cgroup, freezer); - state = freezer->state; - } - spin_unlock_irq(&freezer->lock); - cgroup_unlock(); + /* update states bottom-up */ + cgroup_for_each_descendant_post(pos, cgroup) + update_if_frozen(pos); + update_if_frozen(cgroup); + + rcu_read_unlock(); - seq_puts(m, freezer_state_strs[state]); + seq_puts(m, freezer_state_strs(cgroup_freezer(cgroup)->state)); seq_putc(m, '\n'); return 0; } -static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) +static void freeze_cgroup(struct freezer *freezer) { + struct cgroup *cgroup = freezer->css.cgroup; struct cgroup_iter it; struct task_struct *task; - unsigned int num_cant_freeze_now = 0; cgroup_iter_start(cgroup, &it); - while ((task = cgroup_iter_next(cgroup, &it))) { - if (!freeze_task(task)) - continue; - if (is_task_frozen_enough(task)) - continue; - if (!freezing(task) && !freezer_should_skip(task)) - num_cant_freeze_now++; - } + while ((task = cgroup_iter_next(cgroup, &it))) + freeze_task(task); cgroup_iter_end(cgroup, &it); - - return num_cant_freeze_now ? -EBUSY : 0; } -static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) +static void unfreeze_cgroup(struct freezer *freezer) { + struct cgroup *cgroup = freezer->css.cgroup; struct cgroup_iter it; struct task_struct *task; @@ -300,59 +348,111 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) cgroup_iter_end(cgroup, &it); } -static int freezer_change_state(struct cgroup *cgroup, - enum freezer_state goal_state) +/** + * freezer_apply_state - apply state change to a single cgroup_freezer + * @freezer: freezer to apply state change to + * @freeze: whether to freeze or unfreeze + * @state: CGROUP_FREEZING_* flag to set or clear + * + * Set or clear @state on @cgroup according to @freeze, and perform + * freezing or thawing as necessary. + */ +static void freezer_apply_state(struct freezer *freezer, bool freeze, + unsigned int state) { - struct freezer *freezer; - int retval = 0; - - freezer = cgroup_freezer(cgroup); + /* also synchronizes against task migration, see freezer_attach() */ + lockdep_assert_held(&freezer->lock); - spin_lock_irq(&freezer->lock); + if (!(freezer->state & CGROUP_FREEZER_ONLINE)) + return; - update_if_frozen(cgroup, freezer); - - switch (goal_state) { - case CGROUP_THAWED: - if (freezer->state != CGROUP_THAWED) - atomic_dec(&system_freezing_cnt); - freezer->state = CGROUP_THAWED; - unfreeze_cgroup(cgroup, freezer); - break; - case CGROUP_FROZEN: - if (freezer->state == CGROUP_THAWED) + if (freeze) { + if (!(freezer->state & CGROUP_FREEZING)) atomic_inc(&system_freezing_cnt); - freezer->state = CGROUP_FREEZING; - retval = try_to_freeze_cgroup(cgroup, freezer); - break; - default: - BUG(); + freezer->state |= state; + freeze_cgroup(freezer); + } else { + bool was_freezing = freezer->state & CGROUP_FREEZING; + + freezer->state &= ~state; + + if (!(freezer->state & CGROUP_FREEZING)) { + if (was_freezing) + atomic_dec(&system_freezing_cnt); + freezer->state &= ~CGROUP_FROZEN; + unfreeze_cgroup(freezer); + } } +} +/** + * freezer_change_state - change the freezing state of a cgroup_freezer + * @freezer: freezer of interest + * @freeze: whether to freeze or thaw + * + * Freeze or thaw @freezer according to @freeze. The operations are + * recursive - all descendants of @freezer will be affected. + */ +static void freezer_change_state(struct freezer *freezer, bool freeze) +{ + struct cgroup *pos; + + /* update @freezer */ + spin_lock_irq(&freezer->lock); + freezer_apply_state(freezer, freeze, CGROUP_FREEZING_SELF); spin_unlock_irq(&freezer->lock); - return retval; + /* + * Update all its descendants in pre-order traversal. Each + * descendant will try to inherit its parent's FREEZING state as + * CGROUP_FREEZING_PARENT. + */ + rcu_read_lock(); + cgroup_for_each_descendant_pre(pos, freezer->css.cgroup) { + struct freezer *pos_f = cgroup_freezer(pos); + struct freezer *parent = parent_freezer(pos_f); + + /* + * Our update to @parent->state is already visible which is + * all we need. No need to lock @parent. For more info on + * synchronization, see freezer_post_create(). + */ + spin_lock_irq(&pos_f->lock); + freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING, + CGROUP_FREEZING_PARENT); + spin_unlock_irq(&pos_f->lock); + } + rcu_read_unlock(); } -static int freezer_write(struct cgroup *cgroup, - struct cftype *cft, +static int freezer_write(struct cgroup *cgroup, struct cftype *cft, const char *buffer) { - int retval; - enum freezer_state goal_state; + bool freeze; - if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) - goal_state = CGROUP_THAWED; - else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) - goal_state = CGROUP_FROZEN; + if (strcmp(buffer, freezer_state_strs(0)) == 0) + freeze = false; + else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0) + freeze = true; else return -EINVAL; - if (!cgroup_lock_live_group(cgroup)) - return -ENODEV; - retval = freezer_change_state(cgroup, goal_state); - cgroup_unlock(); - return retval; + freezer_change_state(cgroup_freezer(cgroup), freeze); + return 0; +} + +static u64 freezer_self_freezing_read(struct cgroup *cgroup, struct cftype *cft) +{ + struct freezer *freezer = cgroup_freezer(cgroup); + + return (bool)(freezer->state & CGROUP_FREEZING_SELF); +} + +static u64 freezer_parent_freezing_read(struct cgroup *cgroup, struct cftype *cft) +{ + struct freezer *freezer = cgroup_freezer(cgroup); + + return (bool)(freezer->state & CGROUP_FREEZING_PARENT); } static struct cftype files[] = { @@ -362,23 +462,27 @@ static struct cftype files[] = { .read_seq_string = freezer_read, .write_string = freezer_write, }, + { + .name = "self_freezing", + .flags = CFTYPE_NOT_ON_ROOT, + .read_u64 = freezer_self_freezing_read, + }, + { + .name = "parent_freezing", + .flags = CFTYPE_NOT_ON_ROOT, + .read_u64 = freezer_parent_freezing_read, + }, { } /* terminate */ }; struct cgroup_subsys freezer_subsys = { .name = "freezer", - .create = freezer_create, - .destroy = freezer_destroy, + .css_alloc = freezer_css_alloc, + .css_online = freezer_css_online, + .css_offline = freezer_css_offline, + .css_free = freezer_css_free, .subsys_id = freezer_subsys_id, - .can_attach = freezer_can_attach, + .attach = freezer_attach, .fork = freezer_fork, .base_cftypes = files, - - /* - * freezer subsys doesn't handle hierarchy at all. Frozen state - * should be inherited through the hierarchy - if a parent is - * frozen, all its children should be frozen. Fix it and remove - * the following. - */ - .broken_hierarchy = true, }; |