linux/kernel/freezer.c

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/*
* kernel/freezer.c - Function to freeze a process
*
* Originally from kernel/power/process.c
*/
#include <linux/interrupt.h>
#include <linux/suspend.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
/* protects freezing and frozen transitions */
static DEFINE_SPINLOCK(freezer_lock);
/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
bool was_frozen = false;
long save;
/*
* Enter FROZEN. If NOFREEZE, schedule immediate thawing by
* clearing freezing.
*/
spin_lock_irq(&freezer_lock);
repeat:
if (!freezing(current)) {
spin_unlock_irq(&freezer_lock);
return was_frozen;
}
if (current->flags & PF_NOFREEZE)
clear_freeze_flag(current);
current->flags |= PF_FROZEN;
spin_unlock_irq(&freezer_lock);
save = current->state;
pr_debug("%s entered refrigerator\n", current->comm);
spin_lock_irq(&current->sighand->siglock);
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(&current->sighand->siglock);
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!freezing(current) ||
(check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();
}
/* leave FROZEN */
spin_lock_irq(&freezer_lock);
if (freezing(current))
goto repeat;
current->flags &= ~PF_FROZEN;
spin_unlock_irq(&freezer_lock);
pr_debug("%s left refrigerator\n", current->comm);
/*
* Restore saved task state before returning. The mb'd version
* needs to be used; otherwise, it might silently break
* synchronization which depends on ordered task state change.
*/
set_current_state(save);
return was_frozen;
}
EXPORT_SYMBOL(__refrigerator);
static void fake_signal_wake_up(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&p->sighand->siglock, flags);
signal_wake_up(p, 0);
spin_unlock_irqrestore(&p->sighand->siglock, flags);
}
/**
* freeze_task - send a freeze request to given task
* @p: task to send the request to
* @sig_only: if set, the request will only be sent if the task has the
* PF_FREEZER_NOSIG flag unset
* Return value: 'false', if @sig_only is set and the task has
* PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
*
* The freeze request is sent by setting the tasks's TIF_FREEZE flag and
* either sending a fake signal to it or waking it up, depending on whether
* or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
* has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
* TIF_FREEZE flag will not be set.
*/
bool freeze_task(struct task_struct *p, bool sig_only)
{
unsigned long flags;
bool ret = false;
spin_lock_irqsave(&freezer_lock, flags);
if ((p->flags & PF_NOFREEZE) ||
(sig_only && !should_send_signal(p)))
goto out_unlock;
if (frozen(p))
goto out_unlock;
set_freeze_flag(p);
if (should_send_signal(p)) {
fake_signal_wake_up(p);
/*
* fake_signal_wake_up() goes through p's scheduler
* lock and guarantees that TASK_STOPPED/TRACED ->
* TASK_RUNNING transition can't race with task state
* testing in try_to_freeze_tasks().
*/
} else {
wake_up_state(p, TASK_INTERRUPTIBLE);
}
ret = true;
out_unlock:
spin_unlock_irqrestore(&freezer_lock, flags);
return ret;
}
void __thaw_task(struct task_struct *p)
container freezer: implement freezer cgroup subsystem 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>
2008-10-19 03:27:21 +00:00
{
unsigned long flags;
/*
* Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
* be visible to @p as waking up implies wmb. Waking up inside
* freezer_lock also prevents wakeups from leaking outside
* refrigerator.
*
* If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
* avoid leaving dangling TIF_SIGPENDING behind.
*/
spin_lock_irqsave(&freezer_lock, flags);
clear_freeze_flag(p);
if (frozen(p)) {
wake_up_process(p);
} else {
spin_lock(&p->sighand->siglock);
recalc_sigpending_and_wake(p);
spin_unlock(&p->sighand->siglock);
}
spin_unlock_irqrestore(&freezer_lock, flags);
container freezer: implement freezer cgroup subsystem 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>
2008-10-19 03:27:21 +00:00
}