[PATCH] Cleanup patch for process freezing

1. Establish a simple API for process freezing defined in linux/include/sched.h:

   frozen(process)		Check for frozen process
   freezing(process)		Check if a process is being frozen
   freeze(process)		Tell a process to freeze (go to refrigerator)
   thaw_process(process)	Restart process
   frozen_process(process)	Process is frozen now

2. Remove all references to PF_FREEZE and PF_FROZEN from all
   kernel sources except sched.h

3. Fix numerous locations where try_to_freeze is manually done by a driver

4. Remove the argument that is no longer necessary from two function calls.

5. Some whitespace cleanup

6. Clear potential race in refrigerator (provides an open window of PF_FREEZE
   cleared before setting PF_FROZEN, recalc_sigpending does not check
   PF_FROZEN).

This patch does not address the problem of freeze_processes() violating the rule
that a task may only modify its own flags by setting PF_FREEZE. This is not clean
in an SMP environment. freeze(process) is therefore not SMP safe!

Signed-off-by: Christoph Lameter <christoph@lameter.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 13 insertions, 21 deletions

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 78d92dc6a1ed..0a086640bcfc 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -32,7 +32,7 @@ static inline int freezeable(struct task_struct * p)
 }
 
 /* Refrigerator is place where frozen processes are stored :-). */
-void refrigerator(unsigned long flag)
+void refrigerator(void)
 {
         /* Hmm, should we be allowed to suspend when there are realtime
            processes around? */
@@ -41,14 +41,13 @@ void refrigerator(unsigned long flag)
         current->state = TASK_UNINTERRUPTIBLE;
         pr_debug("%s entered refrigerator\n", current->comm);
         printk("=");
-        current->flags &= ~PF_FREEZE;
 
+        frozen_process(current);
         spin_lock_irq(&current->sighand->siglock);
         recalc_sigpending(); /* We sent fake signal, clean it up */
         spin_unlock_irq(&current->sighand->siglock);
 
-        current->flags |= PF_FROZEN;
-        while (current->flags & PF_FROZEN)
+        while (frozen(current))
                 schedule();
         pr_debug("%s left refrigerator\n", current->comm);
         current->state = save;
@@ -57,10 +56,10 @@ void refrigerator(unsigned long flag)
 /* 0 = success, else # of processes that we failed to stop */
 int freeze_processes(void)
 {
-       int todo;
-       unsigned long start_time;
+        int todo;
+        unsigned long start_time;
         struct task_struct *g, *p;
-        
+
         printk( "Stopping tasks: " );
         start_time = jiffies;
         do {
@@ -70,14 +69,12 @@ int freeze_processes(void)
                         unsigned long flags;
                         if (!freezeable(p))
                                 continue;
-                        if ((p->flags & PF_FROZEN) ||
+                        if ((frozen(p)) ||
                             (p->state == TASK_TRACED) ||
                             (p->state == TASK_STOPPED))
                                 continue;
 
-                        /* FIXME: smp problem here: we may not access other process' flags
-                           without locking */
-                        p->flags |= PF_FREEZE;
+                        freeze(p);
                         spin_lock_irqsave(&p->sighand->siglock, flags);
                         signal_wake_up(p, 0);
                         spin_unlock_irqrestore(&p->sighand->siglock, flags);
@@ -91,7 +88,7 @@ int freeze_processes(void)
                         return todo;
                 }
         } while(todo);
-        
+
         printk( "|\n" );
         BUG_ON(in_atomic());
         return 0;
@@ -106,10 +103,7 @@ void thaw_processes(void)
         do_each_thread(g, p) {
                 if (!freezeable(p))
                         continue;
-                if (p->flags & PF_FROZEN) {
-                        p->flags &= ~PF_FROZEN;
-                        wake_up_process(p);
-                } else
+                if (!thaw_process(p))
                         printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
         } while_each_thread(g, p);
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 76080d142e3d..6fa9ea4ae44c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4174,8 +4174,7 @@ static int migration_thread(void * data)
                 struct list_head *head;
                 migration_req_t *req;
 
-                if (current->flags & PF_FREEZE)
-                        refrigerator(PF_FREEZE);
+                try_to_freeze();
 
                 spin_lock_irq(&rq->lock);
 
diff --git a/kernel/signal.c b/kernel/signal.c
index d1258729a5f9..ca1186eef938 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -213,7 +213,7 @@ static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
 fastcall void recalc_sigpending_tsk(struct task_struct *t)
 {
         if (t->signal->group_stop_count > 0 ||
-            (t->flags & PF_FREEZE) ||
+            (freezing(t)) ||
             PENDING(&t->pending, &t->blocked) ||
             PENDING(&t->signal->shared_pending, &t->blocked))
                 set_tsk_thread_flag(t, TIF_SIGPENDING);
@@ -2231,8 +2231,7 @@ sys_rt_sigtimedwait(const sigset_t __user *uthese,
                         current->state = TASK_INTERRUPTIBLE;
                         timeout = schedule_timeout(timeout);
 
-                        if (current->flags & PF_FREEZE)
-                                refrigerator(PF_FREEZE);
+                        try_to_freeze();
                         spin_lock_irq(&current->sighand->siglock);
                         sig = dequeue_signal(current, &these, &info);
                         current->blocked = current->real_blocked;