![Matt Helsley](/assets/img/avatar_default.png)
This patch implements a new freezer subsystem in the control groups framework. It provides a way to stop and resume execution of all tasks in a cgroup by writing in the cgroup filesystem. The freezer subsystem in the container filesystem defines a file named freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the cgroup. Subsequently writing "RUNNING" will unfreeze the tasks in the cgroup. Reading will return the current state. * Examples of usage : # mkdir /containers/freezer # mount -t cgroup -ofreezer freezer /containers # mkdir /containers/0 # echo $some_pid > /containers/0/tasks to get status of the freezer subsystem : # cat /containers/0/freezer.state RUNNING to freeze all tasks in the container : # echo FROZEN > /containers/0/freezer.state # cat /containers/0/freezer.state FREEZING # cat /containers/0/freezer.state FROZEN to unfreeze all tasks in the container : # echo RUNNING > /containers/0/freezer.state # cat /containers/0/freezer.state RUNNING This is the basic mechanism which should do the right thing for user space task in a simple scenario. It's important to note that freezing can be incomplete. In that case we return EBUSY. This means that some tasks in the cgroup are busy doing something that prevents us from completely freezing the cgroup at this time. After EBUSY, the cgroup will remain partially frozen -- reflected by freezer.state reporting "FREEZING" when read. The state will remain "FREEZING" until one of these things happens: 1) Userspace cancels the freezing operation by writing "RUNNING" to the freezer.state file 2) Userspace retries the freezing operation by writing "FROZEN" to the freezer.state file (writing "FREEZING" is not legal and returns EIO) 3) The tasks that blocked the cgroup from entering the "FROZEN" state disappear from the cgroup's set of tasks. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: export thaw_process] Signed-off-by: Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Matt Helsley <matthltc@us.ibm.com> Acked-by: Serge E. Hallyn <serue@us.ibm.com> Tested-by: Matt Helsley <matthltc@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
155 lines
3.7 KiB
C
155 lines
3.7 KiB
C
/*
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* kernel/freezer.c - Function to freeze a process
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*
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* Originally from kernel/power/process.c
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*/
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#include <linux/interrupt.h>
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#include <linux/suspend.h>
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#include <linux/module.h>
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#include <linux/syscalls.h>
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#include <linux/freezer.h>
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/*
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* freezing is complete, mark current process as frozen
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*/
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static inline void frozen_process(void)
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{
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if (!unlikely(current->flags & PF_NOFREEZE)) {
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current->flags |= PF_FROZEN;
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wmb();
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}
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clear_freeze_flag(current);
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}
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/* Refrigerator is place where frozen processes are stored :-). */
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void refrigerator(void)
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{
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/* Hmm, should we be allowed to suspend when there are realtime
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processes around? */
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long save;
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task_lock(current);
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if (freezing(current)) {
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frozen_process();
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task_unlock(current);
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} else {
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task_unlock(current);
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return;
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}
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save = current->state;
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pr_debug("%s entered refrigerator\n", current->comm);
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spin_lock_irq(¤t->sighand->siglock);
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recalc_sigpending(); /* We sent fake signal, clean it up */
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spin_unlock_irq(¤t->sighand->siglock);
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (!frozen(current))
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break;
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schedule();
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}
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pr_debug("%s left refrigerator\n", current->comm);
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__set_current_state(save);
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}
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EXPORT_SYMBOL(refrigerator);
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static void fake_signal_wake_up(struct task_struct *p)
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{
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unsigned long flags;
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spin_lock_irqsave(&p->sighand->siglock, flags);
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signal_wake_up(p, 0);
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spin_unlock_irqrestore(&p->sighand->siglock, flags);
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}
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/**
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* freeze_task - send a freeze request to given task
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* @p: task to send the request to
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* @sig_only: if set, the request will only be sent if the task has the
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* PF_FREEZER_NOSIG flag unset
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* Return value: 'false', if @sig_only is set and the task has
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* PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
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*
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* The freeze request is sent by setting the tasks's TIF_FREEZE flag and
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* either sending a fake signal to it or waking it up, depending on whether
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* or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
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* has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
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* TIF_FREEZE flag will not be set.
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*/
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bool freeze_task(struct task_struct *p, bool sig_only)
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{
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/*
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* We first check if the task is freezing and next if it has already
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* been frozen to avoid the race with frozen_process() which first marks
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* the task as frozen and next clears its TIF_FREEZE.
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*/
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if (!freezing(p)) {
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rmb();
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if (frozen(p))
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return false;
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if (!sig_only || should_send_signal(p))
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set_freeze_flag(p);
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else
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return false;
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}
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if (should_send_signal(p)) {
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if (!signal_pending(p))
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fake_signal_wake_up(p);
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} else if (sig_only) {
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return false;
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} else {
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wake_up_state(p, TASK_INTERRUPTIBLE);
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}
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return true;
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}
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void cancel_freezing(struct task_struct *p)
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{
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unsigned long flags;
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if (freezing(p)) {
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pr_debug(" clean up: %s\n", p->comm);
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clear_freeze_flag(p);
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spin_lock_irqsave(&p->sighand->siglock, flags);
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recalc_sigpending_and_wake(p);
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spin_unlock_irqrestore(&p->sighand->siglock, flags);
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}
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}
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/*
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* Wake up a frozen process
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*
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* task_lock() is needed to prevent the race with refrigerator() which may
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* occur if the freezing of tasks fails. Namely, without the lock, if the
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* freezing of tasks failed, thaw_tasks() might have run before a task in
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* refrigerator() could call frozen_process(), in which case the task would be
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* frozen and no one would thaw it.
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*/
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int __thaw_process(struct task_struct *p)
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{
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if (frozen(p)) {
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p->flags &= ~PF_FROZEN;
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return 1;
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}
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clear_freeze_flag(p);
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return 0;
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}
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int thaw_process(struct task_struct *p)
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{
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task_lock(p);
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if (__thaw_process(p) == 1) {
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task_unlock(p);
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wake_up_process(p);
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return 1;
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}
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task_unlock(p);
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return 0;
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}
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EXPORT_SYMBOL(thaw_process);
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