sched: fix, always create kernel threads with normal priority

Ensure that the kernel threads are created with the usual nice level
and affinity even if kthreadd's properties were changed from the
default by root.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/kthread.c b/kernel/kthread.c
index dcfe724300eb3cd32c46c2d06de4fc92c7de070b..0ac887882f908502425deeebcda4c678812443cb 100644 (file)
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -15,6 +15,8 @@
 #include <linux/mutex.h>
 #include <asm/semaphore.h>
 
+#define KTHREAD_NICE_LEVEL (-5)
+
 static DEFINE_SPINLOCK(kthread_create_lock);
 static LIST_HEAD(kthread_create_list);
 struct task_struct *kthreadd_task;
@@ -94,10 +96,18 @@ static void create_kthread(struct kthread_create_info *create)
        if (pid < 0) {
                create->result = ERR_PTR(pid);
        } else {
+               struct sched_param param = { .sched_priority = 0 };
                wait_for_completion(&create->started);
                read_lock(&tasklist_lock);
                create->result = find_task_by_pid(pid);
                read_unlock(&tasklist_lock);
+               /*
+                * root may have changed our (kthreadd's) priority or CPU mask.
+                * The kernel thread should not inherit these properties.
+                */
+               sched_setscheduler(create->result, SCHED_NORMAL, &param);
+               set_user_nice(create->result, KTHREAD_NICE_LEVEL);
+               set_cpus_allowed(create->result, CPU_MASK_ALL);
        }
        complete(&create->done);
 }
@@ -221,7 +231,7 @@ int kthreadd(void *unused)
        /* Setup a clean context for our children to inherit. */
        set_task_comm(tsk, "kthreadd");
        ignore_signals(tsk);
-       set_user_nice(tsk, -5);
+       set_user_nice(tsk, KTHREAD_NICE_LEVEL);
        set_cpus_allowed(tsk, CPU_MASK_ALL);
 
        current->flags |= PF_NOFREEZE;