[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>

1 files changed, 59 insertions, 14 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2c69682b0444..e7fd09b0557f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1245,33 +1245,78 @@ extern void normalize_rt_tasks(void);
 
 #endif
 
-/* try_to_freeze
- *
- * Checks whether we need to enter the refrigerator
- * and returns 1 if we did so.
- */
 #ifdef CONFIG_PM
-extern void refrigerator(unsigned long);
+/*
+ * 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;
+}
+
+/*
+ * 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;
+}
+
+/*
+ * freezing is complete, mark process as frozen
+ */
+static inline void frozen_process(struct task_struct *p)
+{
+        p->flags = (p->flags & ~PF_FREEZE) | PF_FROZEN;
+}
+
+extern void refrigerator(void);
 extern int freeze_processes(void);
 extern void thaw_processes(void);
 
-static inline int try_to_freeze(unsigned long refrigerator_flags)
+static inline int try_to_freeze(void)
 {
-        if (unlikely(current->flags & PF_FREEZE)) {
-                refrigerator(refrigerator_flags);
+        if (freezing(current)) {
+                refrigerator();
                 return 1;
         } else
                 return 0;
 }
 #else
-static inline void refrigerator(unsigned long flag) {}
+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 frozen_process(struct task_struct *p) { BUG(); }
+
+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(unsigned long refrigerator_flags)
-{
-        return 0;
-}
+static inline int try_to_freeze(void) { return 0; }
+
 #endif /* CONFIG_PM */
 #endif /* __KERNEL__ */