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linux/kernel/freezer.c at master · fabgithub/linux · GitHub
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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>
/* total number of freezing conditions in effect */
atomic_t
system_freezing_cnt
=
ATOMIC_INIT
(
0
);
EXPORT_SYMBOL
(
system_freezing_cnt
);
/* indicate whether PM freezing is in effect, protected by pm_mutex */
bool
pm_freezing
;
bool
pm_nosig_freezing
;
/* protects freezing and frozen transitions */
static
DEFINE_SPINLOCK
(
freezer_lock
);
/**
* freezing_slow_path - slow path for testing whether a task needs to be frozen
* @p: task to be tested
*
* This function is called by freezing() if system_freezing_cnt isn't zero
* and tests whether @p needs to enter and stay in frozen state. Can be
* called under any context. The freezers are responsible for ensuring the
* target tasks see the updated state.
*/
bool
freezing_slow_path
(
struct
task_struct
*
p
)
{
if
(
p
->
flags
&
PF_NOFREEZE
)
return
false;
if
(
pm_nosig_freezing
||
cgroup_freezing
(
p
))
return
true;
if
(
pm_freezing
&&
!(
p
->
flags
&
PF_KTHREAD
))
return
true;
return
false;
}
EXPORT_SYMBOL
(
freezing_slow_path
);
/* 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
=
current
->
state
;
pr_debug
(
"%s entered refrigerator\n"
,
current
->
comm
);
for
(;;) {
set_current_state
(
TASK_UNINTERRUPTIBLE
);
spin_lock_irq
(
&
freezer_lock
);
current
->
flags
|=
PF_FROZEN
;
if
(!
freezing
(
current
)
||
(
check_kthr_stop
&&
kthread_should_stop
()))
current
->
flags
&= ~
PF_FROZEN
;
spin_unlock_irq
(
&
freezer_lock
);
if
(!(
current
->
flags
&
PF_FROZEN
))
break
;
was_frozen
=
true;
schedule
();
}
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
;
if
(
lock_task_sighand
(
p
,
&
flags
)) {
signal_wake_up
(
p
,
0
);
unlock_task_sighand
(
p
,
&
flags
);
}
}
/**
* freeze_task - send a freeze request to given task
* @p: task to send the request to
*
* If @p is freezing, the freeze request is sent either by sending a fake
* signal (if it's not a kernel thread) or waking it up (if it's a kernel
* thread).
*
* RETURNS:
* %false, if @p is not freezing or already frozen; %true, otherwise
*/
bool
freeze_task
(
struct
task_struct
*
p
)
{
unsigned long
flags
;
/*
* This check can race with freezer_do_not_count, but worst case that
* will result in an extra wakeup being sent to the task. It does not
* race with freezer_count(), the barriers in freezer_count() and
* freezer_should_skip() ensure that either freezer_count() sees
* freezing == true in try_to_freeze() and freezes, or
* freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
* normally.
*/
if
(
freezer_should_skip
(
p
))
return
false;
spin_lock_irqsave
(
&
freezer_lock
,
flags
);
if
(!
freezing
(
p
)
||
frozen
(
p
)) {
spin_unlock_irqrestore
(
&
freezer_lock
,
flags
);
return
false;
}
if
(!(
p
->
flags
&
PF_KTHREAD
))
fake_signal_wake_up
(
p
);
else
wake_up_state
(
p
,
TASK_INTERRUPTIBLE
);
spin_unlock_irqrestore
(
&
freezer_lock
,
flags
);
return
true;
}
void
__thaw_task
(
struct
task_struct
*
p
)
{
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.
*/
spin_lock_irqsave
(
&
freezer_lock
,
flags
);
if
(
frozen
(
p
))
wake_up_process
(
p
);
spin_unlock_irqrestore
(
&
freezer_lock
,
flags
);
}
/**
* set_freezable - make %current freezable
*
* Mark %current freezable and enter refrigerator if necessary.
*/
bool
set_freezable
(
void
)
{
might_sleep
();
/*
* Modify flags while holding freezer_lock. This ensures the
* freezer notices that we aren't frozen yet or the freezing
* condition is visible to try_to_freeze() below.
*/
spin_lock_irq
(
&
freezer_lock
);
current
->
flags
&= ~
PF_NOFREEZE
;
spin_unlock_irq
(
&
freezer_lock
);
return
try_to_freeze
();
}
EXPORT_SYMBOL
(
set_freezable
);
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