Hi,
There is a race condition at wake_up_new_task at CPU hotplug case.
Say do_fork
copy_process (which sets new forked task's current cpu, cpu_allowed)
<-------- the new forked task's current cpu is offline
wake_up_new_task
wake_up_new_task will put the forked task into a dead cpu.
Thanks,
Shaohua
Signed-off-by: Shaohua Li<[email protected]>
---
linux-2.6.11-rc5-mm1-root/kernel/sched.c | 25 +++++++++++++++++++++++--
1 files changed, 23 insertions(+), 2 deletions(-)
diff -puN kernel/sched.c~wake_up_new_task_to_online_cpu kernel/sched.c
--- linux-2.6.11-rc5-mm1/kernel/sched.c~wake_up_new_task_to_online_cpu 2005-05-31 13:39:43.888682784 +0800
+++ linux-2.6.11-rc5-mm1-root/kernel/sched.c 2005-05-31 14:49:58.537958704 +0800
@@ -1412,6 +1412,10 @@ void fastcall sched_fork(task_t *p, int
put_cpu();
}
+#ifdef CONFIG_HOTPLUG_CPU
+static int task_select_online_cpu(int dead_cpu, struct task_struct *tsk);
+#endif
+
/*
* wake_up_new_task - wake up a newly created task for the first time.
*
@@ -1426,9 +1430,20 @@ void fastcall wake_up_new_task(task_t *
runqueue_t *rq, *this_rq;
rq = task_rq_lock(p, &flags);
- BUG_ON(p->state != TASK_RUNNING);
this_cpu = smp_processor_id();
cpu = task_cpu(p);
+#ifdef CONFIG_HOTPLUG_CPU
+ while (!cpu_online(cpu)) {
+ cpu = task_select_online_cpu(cpu, p);
+ set_task_cpu(p, cpu);
+ task_rq_unlock(rq, &flags);
+ /* CPU hotplug might occur here */
+ rq = task_rq_lock(p, &flags);
+ this_cpu = smp_processor_id();
+ cpu = task_cpu(p);
+ }
+#endif
+ BUG_ON(p->state != TASK_RUNNING);
/*
* We decrease the sleep average of forking parents
@@ -4457,7 +4472,7 @@ wait_to_die:
#ifdef CONFIG_HOTPLUG_CPU
/* Figure out where task on dead CPU should go, use force if neccessary. */
-static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
+static int task_select_online_cpu(int dead_cpu, struct task_struct *tsk)
{
int dest_cpu;
cpumask_t mask;
@@ -4486,6 +4501,12 @@ static void move_task_off_dead_cpu(int d
"longer affine to cpu%d\n",
tsk->pid, tsk->comm, dead_cpu);
}
+ return dest_cpu;
+}
+
+static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
+{
+ int dest_cpu = task_select_online_cpu(dead_cpu, tsk);
__migrate_task(tsk, dead_cpu, dest_cpu);
}
_
-
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