kthread: move sched-realeted initialization from kthreadd context

kthreadd is the single thread which implements ths "create" request, move
sched_setscheduler/etc from create_kthread() to kthread_create() to
improve the scalability.

We should be careful with sched_setscheduler(), use _nochek helper.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Vitaliy Gusev <vgusev@openvz.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/kernel/kthread.c b/kernel/kthread.c
index c013bf0..4ebaf85 100644 (file)
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -97,19 +97,10 @@ static void create_kthread(struct kthread_create_info *create)
 
        /* We want our own signal handler (we take no signals by default). */
        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
-       if (pid < 0) {
+       if (pid < 0)
                create->result = ERR_PTR(pid);
-       } else {
-               struct sched_param param = { .sched_priority = 0 };
+       else
                wait_for_completion(&create->started);
-               /*
-                * 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_ptr(create->result, cpu_all_mask);
-       }
        complete(&create->done);
 }
 
@@ -152,11 +143,20 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
        wait_for_completion(&create.done);
 
        if (!IS_ERR(create.result)) {
+               struct sched_param param = { .sched_priority = 0 };
                va_list args;
+
                va_start(args, namefmt);
                vsnprintf(create.result->comm, sizeof(create.result->comm),
                          namefmt, args);
                va_end(args);
+               /*
+                * root may have changed our (kthreadd's) priority or CPU mask.
+                * The kernel thread should not inherit these properties.
+                */
+               sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
+               set_user_nice(create.result, KTHREAD_NICE_LEVEL);
+               set_cpus_allowed_ptr(create.result, cpu_all_mask);
        }
        return create.result;
 }