//SPDX-License-Identifier: GPL-2.0 #include <linux/cgroup.h> #include <linux/sched.h> #include <linux/sched/task.h> #include <linux/sched/signal.h> #include "cgroup-internal.h" #include <trace/events/cgroup.h> /* * Propagate the cgroup frozen state upwards by the cgroup tree. */ static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen) { int desc = 1; /* * If the new state is frozen, some freezing ancestor cgroups may change * their state too, depending on if all their descendants are frozen. * * Otherwise, all ancestor cgroups are forced into the non-frozen state. */ while ((cgrp = cgroup_parent(cgrp))) { if (frozen) { cgrp->freezer.nr_frozen_descendants += desc; if (!test_bit(CGRP_FROZEN, &cgrp->flags) && test_bit(CGRP_FREEZE, &cgrp->flags) && cgrp->freezer.nr_frozen_descendants == cgrp->nr_descendants) { set_bit(CGRP_FROZEN, &cgrp->flags); cgroup_file_notify(&cgrp->events_file); TRACE_CGROUP_PATH(notify_frozen, cgrp, 1); desc++; } } else { cgrp->freezer.nr_frozen_descendants -= desc; if (test_bit(CGRP_FROZEN, &cgrp->flags)) { clear_bit(CGRP_FROZEN, &cgrp->flags); cgroup_file_notify(&cgrp->events_file); TRACE_CGROUP_PATH(notify_frozen, cgrp, 0); desc++; } } } } /* * Revisit the cgroup frozen state. * Checks if the cgroup is really frozen and perform all state transitions. */ void cgroup_update_frozen(struct cgroup *cgrp) { bool frozen; lockdep_assert_held(&css_set_lock); /* * If the cgroup has to be frozen (CGRP_FREEZE bit set), * and all tasks are frozen and/or stopped, let's consider * the cgroup frozen. Otherwise it's not frozen. */ frozen = test_bit(CGRP_FREEZE, &cgrp->flags) && cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp); if (frozen) { /* Already there? */ if (test_bit(CGRP_FROZEN, &cgrp->flags)) return; set_bit(CGRP_FROZEN, &cgrp->flags); } else { /* Already there? */ if (!test_bit(CGRP_FROZEN, &cgrp->flags)) return; clear_bit(CGRP_FROZEN, &cgrp->flags); } cgroup_file_notify(&cgrp->events_file); TRACE_CGROUP_PATH(notify_frozen, cgrp, frozen); /* Update the state of ancestor cgroups. */ cgroup_propagate_frozen(cgrp, frozen); } /* * Increment cgroup's nr_frozen_tasks. */ static void cgroup_inc_frozen_cnt(struct cgroup *cgrp) { cgrp->freezer.nr_frozen_tasks++; } /* * Decrement cgroup's nr_frozen_tasks. */ static void cgroup_dec_frozen_cnt(struct cgroup *cgrp) { cgrp->freezer.nr_frozen_tasks--; WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0); } /* * Enter frozen/stopped state, if not yet there. Update cgroup's counters, * and revisit the state of the cgroup, if necessary. */ void cgroup_enter_frozen(void) { struct cgroup *cgrp; if (current->frozen) return; spin_lock_irq(&css_set_lock); current->frozen = true; cgrp = task_dfl_cgroup(current); cgroup_inc_frozen_cnt(cgrp); cgroup_update_frozen(cgrp); spin_unlock_irq(&css_set_lock); } /* * Conditionally leave frozen/stopped state. Update cgroup's counters, * and revisit the state of the cgroup, if necessary. * * If always_leave is not set, and the cgroup is freezing, * we're racing with the cgroup freezing. In this case, we don't * drop the frozen counter to avoid a transient switch to * the unfrozen state. */ void cgroup_leave_frozen(bool always_leave) { struct cgroup *cgrp; spin_lock_irq(&css_set_lock); cgrp = task_dfl_cgroup(current); if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) { cgroup_dec_frozen_cnt(cgrp); cgroup_update_frozen(cgrp); WARN_ON_ONCE(!current->frozen); current->frozen = false; } else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) { spin_lock(¤t->sighand->siglock); current->jobctl |= JOBCTL_TRAP_FREEZE; set_thread_flag(TIF_SIGPENDING); spin_unlock(¤t->sighand->siglock); } spin_unlock_irq(&css_set_lock); } /* * Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE * jobctl bit. */ static void cgroup_freeze_task(struct task_struct *task, bool freeze) { unsigned long flags; /* If the task is about to die, don't bother with freezing it. */ if (!lock_task_sighand(task, &flags)) return; if (freeze) { task->jobctl |= JOBCTL_TRAP_FREEZE; signal_wake_up(task, false); } else { task->jobctl &= ~JOBCTL_TRAP_FREEZE; wake_up_process(task); } unlock_task_sighand(task, &flags); } /* * Freeze or unfreeze all tasks in the given cgroup. */ static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze) { struct css_task_iter it; struct task_struct *task; lockdep_assert_held(&cgroup_mutex); spin_lock_irq(&css_set_lock); if (freeze) set_bit(CGRP_FREEZE, &cgrp->flags); else clear_bit(CGRP_FREEZE, &cgrp->flags); spin_unlock_irq(&css_set_lock); if (freeze) TRACE_CGROUP_PATH(freeze, cgrp); else TRACE_CGROUP_PATH(unfreeze, cgrp); css_task_iter_start(&cgrp->self, 0, &it); while ((task = css_task_iter_next(&it))) { /* * Ignore kernel threads here. Freezing cgroups containing * kthreads isn't supported. */ if (task->flags & PF_KTHREAD) continue; cgroup_freeze_task(task, freeze); } css_task_iter_end(&it); /* * Cgroup state should be revisited here to cover empty leaf cgroups * and cgroups which descendants are already in the desired state. */ spin_lock_irq(&css_set_lock); if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants) cgroup_update_frozen(cgrp); spin_unlock_irq(&css_set_lock); } /* * Adjust the task state (freeze or unfreeze) and revisit the state of * source and destination cgroups. */ void cgroup_freezer_migrate_task(struct task_struct *task, struct cgroup *src, struct cgroup *dst) { lockdep_assert_held(&css_set_lock); /* * Kernel threads are not supposed to be frozen at all. */ if (task->flags & PF_KTHREAD) return; /* * It's not necessary to do changes if both of the src and dst cgroups * are not freezing and task is not frozen. */ if (!test_bit(CGRP_FREEZE, &src->flags) && !test_bit(CGRP_FREEZE, &dst->flags) && !task->frozen) return; /* * Adjust counters of freezing and frozen tasks. * Note, that if the task is frozen, but the destination cgroup is not * frozen, we bump both counters to keep them balanced. */ if (task->frozen) { cgroup_inc_frozen_cnt(dst); cgroup_dec_frozen_cnt(src); } cgroup_update_frozen(dst); cgroup_update_frozen(src); /* * Force the task to the desired state. */ cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags)); } void cgroup_freeze(struct cgroup *cgrp, bool freeze) { struct cgroup_subsys_state *css; struct cgroup *dsct; bool applied = false; lockdep_assert_held(&cgroup_mutex); /* * Nothing changed? Just exit. */ if (cgrp->freezer.freeze == freeze) return; cgrp->freezer.freeze = freeze; /* * Propagate changes downwards the cgroup tree. */ css_for_each_descendant_pre(css, &cgrp->self) { dsct = css->cgroup; if (cgroup_is_dead(dsct)) continue; if (freeze) { dsct->freezer.e_freeze++; /* * Already frozen because of ancestor's settings? */ if (dsct->freezer.e_freeze > 1) continue; } else { dsct->freezer.e_freeze--; /* * Still frozen because of ancestor's settings? */ if (dsct->freezer.e_freeze > 0) continue; WARN_ON_ONCE(dsct->freezer.e_freeze < 0); } /* * Do change actual state: freeze or unfreeze. */ cgroup_do_freeze(dsct, freeze); applied = true; } /* * Even if the actual state hasn't changed, let's notify a user. * The state can be enforced by an ancestor cgroup: the cgroup * can already be in the desired state or it can be locked in the * opposite state, so that the transition will never happen. * In both cases it's better to notify a user, that there is * nothing to wait for. */ if (!applied) { TRACE_CGROUP_PATH(notify_frozen, cgrp, test_bit(CGRP_FROZEN, &cgrp->flags)); cgroup_file_notify(&cgrp->events_file); } }