kernel-ark/include/linux/freezer.h
Rafael J. Wysocki 8314418629 Freezer: make kernel threads nonfreezable by default
Currently, the freezer treats all tasks as freezable, except for the kernel
threads that explicitly set the PF_NOFREEZE flag for themselves.  This
approach is problematic, since it requires every kernel thread to either
set PF_NOFREEZE explicitly, or call try_to_freeze(), even if it doesn't
care for the freezing of tasks at all.

It seems better to only require the kernel threads that want to or need to
be frozen to use some freezer-related code and to remove any
freezer-related code from the other (nonfreezable) kernel threads, which is
done in this patch.

The patch causes all kernel threads to be nonfreezable by default (ie.  to
have PF_NOFREEZE set by default) and introduces the set_freezable()
function that should be called by the freezable kernel threads in order to
unset PF_NOFREEZE.  It also makes all of the currently freezable kernel
threads call set_freezable(), so it shouldn't cause any (intentional)
change of behaviour to appear.  Additionally, it updates documentation to
describe the freezing of tasks more accurately.

[akpm@linux-foundation.org: build fixes]
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-17 10:23:02 -07:00

148 lines
3.8 KiB
C++

/* Freezer declarations */
#ifndef FREEZER_H_INCLUDED
#define FREEZER_H_INCLUDED
#include <linux/sched.h>
#ifdef CONFIG_PM
/*
* Check if a process has been frozen
*/
static inline int frozen(struct task_struct *p)
{
return p->flags & PF_FROZEN;
}
/*
* Check if there is a request to freeze a process
*/
static inline int freezing(struct task_struct *p)
{
return test_tsk_thread_flag(p, TIF_FREEZE);
}
/*
* Request that a process be frozen
*/
static inline void freeze(struct task_struct *p)
{
set_tsk_thread_flag(p, TIF_FREEZE);
}
/*
* Sometimes we may need to cancel the previous 'freeze' request
*/
static inline void do_not_freeze(struct task_struct *p)
{
clear_tsk_thread_flag(p, TIF_FREEZE);
}
/*
* Wake up a frozen process
*
* task_lock() is taken to prevent the race with refrigerator() which may
* occur if the freezing of tasks fails. Namely, without the lock, if the
* freezing of tasks failed, thaw_tasks() might have run before a task in
* refrigerator() could call frozen_process(), in which case the task would be
* frozen and no one would thaw it.
*/
static inline int thaw_process(struct task_struct *p)
{
task_lock(p);
if (frozen(p)) {
p->flags &= ~PF_FROZEN;
task_unlock(p);
wake_up_process(p);
return 1;
}
clear_tsk_thread_flag(p, TIF_FREEZE);
task_unlock(p);
return 0;
}
extern void refrigerator(void);
extern int freeze_processes(void);
extern void thaw_processes(void);
static inline int try_to_freeze(void)
{
if (freezing(current)) {
refrigerator();
return 1;
} else
return 0;
}
/*
* The PF_FREEZER_SKIP flag should be set by a vfork parent right before it
* calls wait_for_completion(&vfork) and reset right after it returns from this
* function. Next, the parent should call try_to_freeze() to freeze itself
* appropriately in case the child has exited before the freezing of tasks is
* complete. However, we don't want kernel threads to be frozen in unexpected
* places, so we allow them to block freeze_processes() instead or to set
* PF_NOFREEZE if needed and PF_FREEZER_SKIP is only set for userland vfork
* parents. Fortunately, in the ____call_usermodehelper() case the parent won't
* really block freeze_processes(), since ____call_usermodehelper() (the child)
* does a little before exec/exit and it can't be frozen before waking up the
* parent.
*/
/*
* If the current task is a user space one, tell the freezer not to count it as
* freezable.
*/
static inline void freezer_do_not_count(void)
{
if (current->mm)
current->flags |= PF_FREEZER_SKIP;
}
/*
* If the current task is a user space one, tell the freezer to count it as
* freezable again and try to freeze it.
*/
static inline void freezer_count(void)
{
if (current->mm) {
current->flags &= ~PF_FREEZER_SKIP;
try_to_freeze();
}
}
/*
* Check if the task should be counted as freezeable by the freezer
*/
static inline int freezer_should_skip(struct task_struct *p)
{
return !!(p->flags & PF_FREEZER_SKIP);
}
/*
* Tell the freezer that the current task should be frozen by it
*/
static inline void set_freezable(void)
{
current->flags &= ~PF_NOFREEZE;
}
#else
static inline int frozen(struct task_struct *p) { return 0; }
static inline int freezing(struct task_struct *p) { return 0; }
static inline void freeze(struct task_struct *p) { BUG(); }
static inline int thaw_process(struct task_struct *p) { return 1; }
static inline void refrigerator(void) {}
static inline int freeze_processes(void) { BUG(); return 0; }
static inline void thaw_processes(void) {}
static inline int try_to_freeze(void) { return 0; }
static inline void freezer_do_not_count(void) {}
static inline void freezer_count(void) {}
static inline int freezer_should_skip(struct task_struct *p) { return 0; }
static inline void set_freezable(void) {}
#endif
#endif /* FREEZER_H_INCLUDED */