Merge to Fedora kernel-2.6.17-1.2187_FC5 patched with stable patch-2.6.17.13-vs2...

[linux-2.6.git] / kernel / timer.c

diff --git a/kernel/timer.c b/kernel/timer.c
index 2f8cdbe..20a4bca 100644 (file)
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -543,6 +543,22 @@ found:
        }
        spin_unlock(&base->lock);
 
+       /*
+        * It can happen that other CPUs service timer IRQs and increment
+        * jiffies, but we have not yet got a local timer tick to process
+        * the timer wheels.  In that case, the expiry time can be before
+        * jiffies, but since the high-resolution timer here is relative to
+        * jiffies, the default expression when high-resolution timers are
+        * not active,
+        *
+        *   time_before(MAX_JIFFY_OFFSET + jiffies, expires)
+        *
+        * would falsely evaluate to true.  If that is the case, just
+        * return jiffies so that we can immediately fire the local timer
+        */
+       if (time_before(expires, jiffies))
+               return jiffies;
+
        /*
         * It can happen that other CPUs service timer IRQs and increment
         * jiffies, but we have not yet got a local timer tick to process
@@ -971,46 +987,18 @@ asmlinkage long sys_getpid(void)
 }
 
 /*
- * Accessing ->group_leader->real_parent is not SMP-safe, it could
- * change from under us. However, rather than getting any lock
- * we can use an optimistic algorithm: get the parent
- * pid, and go back and check that the parent is still
- * the same. If it has changed (which is extremely unlikely
- * indeed), we just try again..
- *
- * NOTE! This depends on the fact that even if we _do_
- * get an old value of "parent", we can happily dereference
- * the pointer (it was and remains a dereferencable kernel pointer
- * no matter what): we just can't necessarily trust the result
- * until we know that the parent pointer is valid.
- *
- * NOTE2: ->group_leader never changes from under us.
+ * Accessing ->real_parent is not SMP-safe, it could
+ * change from under us. However, we can use a stale
+ * value of ->real_parent under rcu_read_lock(), see
+ * release_task()->call_rcu(delayed_put_task_struct).
  */
 asmlinkage long sys_getppid(void)
 {
        int pid;
-       struct task_struct *me = current;
-       struct task_struct *parent;
 
-       parent = me->group_leader->real_parent;
-       for (;;) {
-               pid = parent->tgid;
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
-{
-               struct task_struct *old = parent;
-
-               /*
-                * Make sure we read the pid before re-reading the
-                * parent pointer:
-                */
-               smp_rmb();
-               parent = me->group_leader->real_parent;
-               if (old != parent)
-                       continue;
-}
-#endif
-               break;
-       }
+       rcu_read_lock();
+       pid = rcu_dereference(current->real_parent)->tgid;
+       rcu_read_unlock();
        return vx_map_pid(pid);
 }
 
@@ -1025,7 +1013,7 @@ asmlinkage long do_getxpid(long *ppid)
        *ppid = sys_getppid();
        return sys_getpid();
 }
-  
+
 #else /* _alpha_ */
 
 asmlinkage long sys_getuid(void)