[PATCH] sched: new task fix

Rusty noticed that we update the parent ->avg_sleep without holding the
runqueue lock. Also the code needed cleanups.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index c4ba3805a4fb6145401accee902c5d5233311487..5f21f757be1d47f974aa8c8842fd8bd804c84041 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1341,7 +1341,7 @@ void fastcall wake_up_new_task(task_t * p, unsigned long clone_flags)
 {
        unsigned long flags;
        int this_cpu, cpu;
-       runqueue_t *rq;
+       runqueue_t *rq, *this_rq;
 
        rq = task_rq_lock(p, &flags);
        cpu = task_cpu(p);
@@ -1383,8 +1383,15 @@ void fastcall wake_up_new_task(task_t * p, unsigned long clone_flags)
                } else
                        /* Run child last */
                        __activate_task(p, rq);
+               /*
+                * We skip the following code due to cpu == this_cpu
+                *
+                *   task_rq_unlock(rq, &flags);
+                *   this_rq = task_rq_lock(current, &flags);
+                */
+               this_rq = rq;
        } else {
-               runqueue_t *this_rq = cpu_rq(this_cpu);
+               this_rq = cpu_rq(this_cpu);
 
                /*
                 * Not the local CPU - must adjust timestamp. This should
@@ -1396,18 +1403,17 @@ void fastcall wake_up_new_task(task_t * p, unsigned long clone_flags)
                if (TASK_PREEMPTS_CURR(p, rq))
                        resched_task(rq->curr);
 
-               current->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(current) *
-                       PARENT_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
                schedstat_inc(rq, wunt_moved);
-       }
-
-       if (unlikely(cpu != this_cpu)) {
+               /*
+                * Parent and child are on different CPUs, now get the
+                * parent runqueue to update the parent's ->sleep_avg:
+                */
                task_rq_unlock(rq, &flags);
-               rq = task_rq_lock(current, &flags);
+               this_rq = task_rq_lock(current, &flags);
        }
        current->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(current) *
                PARENT_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);
-       task_rq_unlock(rq, &flags);
+       task_rq_unlock(this_rq, &flags);
 }
 
 /*