Re: [RFC] Fix SMP brokenness for PF_FREEZE and make freezing usable for other purposes

[Kirill Korotaev <dev@sw.ru>]

commented with <<<< inside

>>Approach seems okay... Perhaps better place is something like
>>kernel/freezer.c so it stays separate file? It is not really scheduler
>>core, and it is only conditionally compiled...
> 
> 
> There is already lots of other conditional code in kernel/sched.c and this 
> is just one function. It is scheduler like and uses scheduler variables 
> since it suspends a process. So lets move it there.
> 
> I think this is as far as I can take it. Could you test this and see 
> if it works okay?
> 
> For suspension for migration do:
> 
> 1. down(&freezer_sem)
> 
> 2. Signal processes to sleep (see kernel/power/process.c). Basically
>    set the TIF_FREEZE and may be do the fake signal thing.
> 
> 3. If all processes have PF_FROZEN set then they are asleep.
> 
> 4. Do migration things
> 
> 5. complete_all(&thaw)
> 
> 6. up(&freezer_sem)
> 
> ----
> Revise handling of freezing in the suspend code
> 
> The current suspend code modifies thread flags from outside the context of process.
> This creates a SMP race.
> 
> The patch fixes that by introducing a TIF_FREEZE flag (for all arches). Also
> 
> - Uses a completion handler instead of waiting in a schedule loop in the refrigerator.
> 
> - Introduces a semaphore freezer_sem to provide a way that multiple kernel
>   subsystems can use the freezing ability without interfering with one another.
> 
> - Include necessary definitions for the migration code if CONFIG_MIGRATE is set.
> 
> - Removes PF_FREEZE
> 
> Signed-off-by: Christoph Lameter <christoph@lameter.com>
> 
> Index: linux-2.6.12/include/linux/sched.h
> ===================================================================
> --- linux-2.6.12.orig/include/linux/sched.h	2005-06-27 05:20:15.000000000 +0000
> +++ linux-2.6.12/include/linux/sched.h	2005-06-27 05:33:46.000000000 +0000
> @@ -804,7 +804,6 @@ do { if (atomic_dec_and_test(&(tsk)->usa
>  #define PF_MEMALLOC	0x00000800	/* Allocating memory */
>  #define PF_FLUSHER	0x00001000	/* responsible for disk writeback */
>  #define PF_USED_MATH	0x00002000	/* if unset the fpu must be initialized before use */
> -#define PF_FREEZE	0x00004000	/* this task is being frozen for suspend now */
>  #define PF_NOFREEZE	0x00008000	/* this thread should not be frozen */
>  #define PF_FROZEN	0x00010000	/* frozen for system suspend */
>  #define PF_FSTRANS	0x00020000	/* inside a filesystem transaction */
> @@ -1265,78 +1264,37 @@ extern void normalize_rt_tasks(void);
>  
>  #endif
>  
> -#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 p->flags & PF_FREEZE;
> -}
> +#if defined(CONFIG_PM) || defined(CONFIG_MIGRATE)
<<<< why not to make a single option CONFIG_REFRIGERATOR? It looks to be 
a more robust way, since there are multiple users of it.
> +extern struct semaphore freezer_sem;
> +extern struct completion thaw;
>  
> -/*
> - * Request that a process be frozen
> - * FIXME: SMP problem. We may not modify other process' flags!
> - */
> -static inline void freeze(struct task_struct *p)
> -{
> -	p->flags |= PF_FREEZE;
> -}
> -
> -/*
> - * Wake up a frozen process
> - */
> -static inline int thaw_process(struct task_struct *p)
> -{
> -	if (frozen(p)) {
> -		p->flags &= ~PF_FROZEN;
> -		wake_up_process(p);
> -		return 1;
> -	}
> -	return 0;
> -}
> +extern void refrigerator(void);
>  
> -/*
> - * freezing is complete, mark process as frozen
> - */
> -static inline void frozen_process(struct task_struct *p)
> +static inline int freezing(struct task_struct *p)
>  {
> -	p->flags = (p->flags & ~PF_FREEZE) | PF_FROZEN;
> +	return test_ti_thread_flag(p->thread_info, TIF_FREEZE);
>  }
>  
> -extern void refrigerator(void);
> -extern int freeze_processes(void);
> -extern void thaw_processes(void);
> -
>  static inline int try_to_freeze(void)
>  {
> -	if (freezing(current)) {
> +	if (test_thread_flag(TIF_FREEZE)) {
>  		refrigerator();
>  		return 1;
>  	} else
>  		return 0;
>  }
>  #else
> -static inline int frozen(struct task_struct *p) { return 0; }
> +static inline void refrigerator(void) {}
>  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 frozen_process(struct task_struct *p) { BUG(); }
> +static inline int try_to_freeze(void) { return 0; }
> +#endif
>  
> -static inline void refrigerator(void) {}
> +#ifdef CONFIG_PM
<<<< is it intentionaly? or you just lost CONFIG_MIGRATE?
> +extern int freeze_processes(void);
> +extern void thaw_processes(void);
> +#else
>  static inline int freeze_processes(void) { BUG(); return 0; }
>  static inline void thaw_processes(void) {}
> -
> -static inline int try_to_freeze(void) { return 0; }
> -
>  #endif /* CONFIG_PM */
>  #endif /* __KERNEL__ */
>  
> Index: linux-2.6.12/kernel/power/process.c
> ===================================================================
> --- linux-2.6.12.orig/kernel/power/process.c	2005-06-27 05:20:15.000000000 +0000
> +++ linux-2.6.12/kernel/power/process.c	2005-06-27 15:07:46.000000000 +0000
> @@ -18,7 +18,6 @@
>   */
>  #define TIMEOUT	(6 * HZ)
>  
> -
>  static inline int freezeable(struct task_struct * p)
>  {
>  	if ((p == current) || 
> @@ -31,28 +30,6 @@ static inline int freezeable(struct task
>  	return 1;
>  }
>  
> -/* Refrigerator is place where frozen processes are stored :-). */
> -void refrigerator(void)
> -{
> -	/* Hmm, should we be allowed to suspend when there are realtime
> -	   processes around? */
> -	long save;
> -	save = current->state;
> -	current->state = TASK_UNINTERRUPTIBLE;
> -	pr_debug("%s entered refrigerator\n", current->comm);
> -	printk("=");
> -
> -	frozen_process(current);
> -	spin_lock_irq(&current->sighand->siglock);
> -	recalc_sigpending(); /* We sent fake signal, clean it up */
> -	spin_unlock_irq(&current->sighand->siglock);
> -
> -	while (frozen(current))
> -		schedule();
> -	pr_debug("%s left refrigerator\n", current->comm);
> -	current->state = save;
> -}
> -
>  /* 0 = success, else # of processes that we failed to stop */
>  int freeze_processes(void)
>  {
> @@ -60,6 +37,7 @@ int freeze_processes(void)
>  	unsigned long start_time;
>  	struct task_struct *g, *p;
>  
> +	down(&freezer_sem);
>  	printk( "Stopping tasks: " );
>  	start_time = jiffies;
>  	do {
> @@ -69,12 +47,12 @@ int freeze_processes(void)
>  			unsigned long flags;
>  			if (!freezeable(p))
>  				continue;
> -			if ((frozen(p)) ||
> +			if ((p->flags & PF_FROZEN) ||
>  			    (p->state == TASK_TRACED) ||
>  			    (p->state == TASK_STOPPED))
>  				continue;
>  
> -			freeze(p);
> +			set_thread_flag(TIF_FREEZE);
>  			spin_lock_irqsave(&p->sighand->siglock, flags);
>  			signal_wake_up(p, 0);
>  			spin_unlock_irqrestore(&p->sighand->siglock, flags);
> @@ -96,20 +74,6 @@ int freeze_processes(void)
>  
>  void thaw_processes(void)
>  {
> -	struct task_struct *g, *p;
> -
> -	printk( "Restarting tasks..." );
> -	read_lock(&tasklist_lock);
> -	do_each_thread(g, p) {
> -		if (!freezeable(p))
> -			continue;
> -		if (!thaw_process(p))
> -			printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
> -	} while_each_thread(g, p);
> -
> -	read_unlock(&tasklist_lock);
> -	schedule();
> -	printk( " done\n" );
> +	complete_all(&thaw);
> +	up(&freezer_sem);
>  }
> -
> -EXPORT_SYMBOL(refrigerator);
> Index: linux-2.6.12/include/asm-x86_64/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-x86_64/thread_info.h	2005-06-27 05:20:15.000000000 +0000
> +++ linux-2.6.12/include/asm-x86_64/thread_info.h	2005-06-27 05:37:24.000000000 +0000
> @@ -108,6 +108,7 @@ static inline struct thread_info *stack_
>  #define TIF_FORK		18	/* ret_from_fork */
>  #define TIF_ABI_PENDING		19
>  #define TIF_MEMDIE		20
> +#define TIF_FREEZE		21	/* Freeze process */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-ia64/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-ia64/thread_info.h	2005-06-27 05:20:15.000000000 +0000
> +++ linux-2.6.12/include/asm-ia64/thread_info.h	2005-06-27 05:26:12.000000000 +0000
> @@ -76,6 +76,7 @@ struct thread_info {
>  #define TIF_SIGDELAYED		5	/* signal delayed from MCA/INIT/NMI/PMI context */
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		17
> +#define TIF_FREEZE		18	/* Freeze process */
>  
>  #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
>  #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
> Index: linux-2.6.12/include/asm-i386/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-i386/thread_info.h	2005-06-27 05:20:15.000000000 +0000
> +++ linux-2.6.12/include/asm-i386/thread_info.h	2005-06-27 05:25:49.000000000 +0000
> @@ -143,6 +143,7 @@ register unsigned long current_stack_poi
>  #define TIF_SECCOMP		8	/* secure computing */
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		17
> +#define TIF_FREEZE		18	/* Freeze thread */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-xtensa/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-xtensa/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-xtensa/thread_info.h	2005-06-27 05:36:54.000000000 +0000
> @@ -118,6 +118,7 @@ static inline struct thread_info *curren
>  #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
>  #define TIF_IRET		5	/* return with iret */
>  #define TIF_MEMDIE		6
> +#define TIF_FREEZE		7
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-h8300/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-h8300/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-h8300/thread_info.h	2005-06-27 05:25:25.000000000 +0000
> @@ -94,6 +94,7 @@ static inline struct thread_info *curren
>  #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
>  					   TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		5
> +#define TIF_FREEZE		6
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-ppc/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-ppc/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-ppc/thread_info.h	2005-06-27 05:28:53.000000000 +0000
> @@ -80,6 +80,7 @@ static inline struct thread_info *curren
>  #define TIF_MEMDIE		5
>  #define TIF_SYSCALL_AUDIT       6       /* syscall auditing active */
>  #define TIF_SECCOMP             7      /* secure computing */
> +#define TIF_FREEZE		8
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-sh64/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-sh64/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-sh64/thread_info.h	2005-06-27 05:35:02.000000000 +0000
> @@ -80,6 +80,7 @@ static inline struct thread_info *curren
>  #define TIF_SIGPENDING		2	/* signal pending */
>  #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
>  #define TIF_MEMDIE		4
> +#define TIF_FREEZE		5
>  
>  
>  #endif /* __KERNEL__ */
> Index: linux-2.6.12/include/asm-alpha/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-alpha/thread_info.h	2005-06-17 19:48:29.000000000 +0000
> +++ linux-2.6.12/include/asm-alpha/thread_info.h	2005-06-27 05:23:06.000000000 +0000
> @@ -78,6 +78,7 @@ register struct thread_info *__current_t
>  #define TIF_UAC_NOFIX		7
>  #define TIF_UAC_SIGBUS		8
>  #define TIF_MEMDIE		9
> +#define TIF_FREEZE		10
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-sparc/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-sparc/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-sparc/thread_info.h	2005-06-27 05:35:23.000000000 +0000
> @@ -139,6 +139,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
>  #define TIF_POLLING_NRFLAG	9	/* true if poll_idle() is polling
>  					 * TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		10
> +#define TIF_FREEZE		11
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-frv/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-frv/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-frv/thread_info.h	2005-06-27 05:25:02.000000000 +0000
> @@ -133,6 +133,7 @@ register struct thread_info *__current_t
>  #define TIF_IRET		5	/* return with iret */
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		17	/* OOM killer killed process */
> +#define TIF_FREEZE		18
>  
>  #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-parisc/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-parisc/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-parisc/thread_info.h	2005-06-27 05:28:34.000000000 +0000
> @@ -64,6 +64,7 @@ struct thread_info {
>  #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_32BIT               5       /* 32 bit binary */
>  #define TIF_MEMDIE		6
> +#define TIF_FREEZE		7
>  
>  #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-m68knommu/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-m68knommu/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-m68knommu/thread_info.h	2005-06-27 05:27:13.000000000 +0000
> @@ -91,6 +91,7 @@ static inline struct thread_info *curren
>  #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
>  					   TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		5
> +#define TIF_FREEZE		6
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-m68k/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-m68k/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-m68k/thread_info.h	2005-06-27 05:26:49.000000000 +0000
> @@ -49,6 +49,7 @@ struct thread_info {
>  #define TIF_SIGPENDING		3	/* signal pending */
>  #define TIF_NEED_RESCHED	4	/* rescheduling necessary */
>  #define TIF_MEMDIE		5
> +#define TIF_FREEZE		6
>  
>  extern int thread_flag_fixme(void);
>  
> Index: linux-2.6.12/include/asm-sh/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-sh/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-sh/thread_info.h	2005-06-27 05:34:43.000000000 +0000
> @@ -84,6 +84,7 @@ static inline struct thread_info *curren
>  #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
>  #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		18
> +#define TIF_FREEZE		19
>  #define TIF_USERSPACE		31	/* true if FS sets userspace */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-s390/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-s390/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-s390/thread_info.h	2005-06-27 05:34:19.000000000 +0000
> @@ -102,6 +102,7 @@ static inline struct thread_info *curren
>  					   TIF_NEED_RESCHED */
>  #define TIF_31BIT		18	/* 32bit process */ 
>  #define TIF_MEMDIE		19
> +#define TIF_FREEZE		20
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-arm/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-arm/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-arm/thread_info.h	2005-06-27 05:23:34.000000000 +0000
> @@ -132,6 +132,7 @@ extern void iwmmxt_task_release(struct t
>  #define TIF_POLLING_NRFLAG	16
>  #define TIF_USING_IWMMXT	17
>  #define TIF_MEMDIE		18
> +#define TIF_FREEZE		19
>  
>  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
>  #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
> Index: linux-2.6.12/include/asm-v850/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-v850/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-v850/thread_info.h	2005-06-27 05:36:25.000000000 +0000
> @@ -85,6 +85,7 @@ struct thread_info {
>  #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
>  					   TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		5
> +#define TIF_FREEZE		6
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-mips/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-mips/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-mips/thread_info.h	2005-06-27 05:27:41.000000000 +0000
> @@ -117,6 +117,7 @@ register struct thread_info *__current_t
>  #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
>  #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		18
> +#define TIF_FREEZE		19
>  #define TIF_SYSCALL_TRACE	31	/* syscall trace active */
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-cris/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-cris/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-cris/thread_info.h	2005-06-27 05:24:28.000000000 +0000
> @@ -86,6 +86,7 @@ struct thread_info {
>  #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  #define TIF_MEMDIE		17
> +#define TIF_FREEZE		18
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-arm26/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-arm26/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-arm26/thread_info.h	2005-06-27 05:24:02.000000000 +0000
> @@ -127,6 +127,7 @@ extern void free_thread_info(struct thre
>  #define TIF_USED_FPU		16
>  #define TIF_POLLING_NRFLAG	17
>  #define TIF_MEMDIE		18
> +#define TIF_FREEZE		19
>  
>  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
>  #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
> Index: linux-2.6.12/include/asm-sparc64/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-sparc64/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-sparc64/thread_info.h	2005-06-27 05:35:45.000000000 +0000
> @@ -229,6 +229,7 @@ register struct thread_info *current_thr
>   */
>  #define TIF_ABI_PENDING		12
>  #define TIF_MEMDIE		13
> +#define TIF_FREEZE		14
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-m32r/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-m32r/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-m32r/thread_info.h	2005-06-27 05:26:33.000000000 +0000
> @@ -156,6 +156,7 @@ static inline unsigned int get_thread_fa
>  #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>  					/* 31..28 fault code */
>  #define TIF_MEMDIE		17
> +#define TIF_FREEZE		18
>  
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
>  #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
> Index: linux-2.6.12/include/asm-ppc64/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-ppc64/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-ppc64/thread_info.h	2005-06-27 05:29:13.000000000 +0000
> @@ -102,6 +102,7 @@ static inline struct thread_info *curren
>  #define TIF_SINGLESTEP		9	/* singlestepping active */
>  #define TIF_MEMDIE		10
>  #define TIF_SECCOMP		11	/* secure computing */
> +#define TIF_FREEZE		12
>  
>  /* as above, but as bit values */
>  #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
> Index: linux-2.6.12/include/asm-um/thread_info.h
> ===================================================================
> --- linux-2.6.12.orig/include/asm-um/thread_info.h	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/include/asm-um/thread_info.h	2005-06-27 05:36:07.000000000 +0000
> @@ -72,6 +72,7 @@ static inline struct thread_info *curren
>  #define TIF_RESTART_BLOCK 	4
>  #define TIF_MEMDIE	 	5
>  #define TIF_SYSCALL_AUDIT	6
> +#define TIF_FREEZE		7
>  
>  #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
>  #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
> Index: linux-2.6.12/kernel/sched.c
> ===================================================================
> --- linux-2.6.12.orig/kernel/sched.c	2005-06-27 02:23:01.000000000 +0000
> +++ linux-2.6.12/kernel/sched.c	2005-06-27 15:08:19.000000000 +0000
> @@ -5203,6 +5203,25 @@ void __init sched_init(void)
>  	init_idle(current, smp_processor_id());
>  }
>  
> +#if defined(CONFIG_PM) || defined(CONFIG_MIGRATE)
> +DECLARE_MUTEX(freezer_sem);
> +DECLARE_COMPLETION(thaw);
> +
> +void refrigerator(void)
> +{
> +	current->flags |= PF_FROZEN;
> +	clear_thread_flag(TIF_FREEZE);
> +	/* A fake signal 0 may have been sent. Recalculate sigpending */
> +	spin_lock_irq(&current->sighand->siglock);
> +	recalc_sigpending();
> +	spin_unlock_irq(&current->sighand->siglock);
> +	wait_for_completion(&thaw);
> +	current->flags &= ~PF_FROZEN;
<<<< I still think this refrigerator is racy with freeze_processes():
<<<< scenarios:
<<<< scenario 1
<<<<
task1 -> freeze_processes():			taskXXX ->refrigerator()
   checked (task->flags & PF_FROZEN) == 0	cur->flags |= PF_FROZEN
						clear TIF_FREEZE
						<sleep on thaw>
   set TIF_FREEZING
						clear PF_FROZEN

<<<< so the task awakes with TIF_FREEZE flag set!!!

<<<< scenario 2
<<<< look at error path in freeze_processes (on timeout), it is broken 
as well. You need to wakeup tasks there...

<<<< ------------------------------
> +}
> +EXPORT_SYMBOL(refrigerator);
> +#endif
> +
> +
>  #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
>  void __might_sleep(char *file, int line)
>  {
> -
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