kthreads: simplify the startup synchronization

We use two completions two create the kernel thread, this is a bit ugly.
kthread() wakes up create_kthread() via ->started, then create_kthread()
wakes up the caller kthread_create() via ->done.  But kthread() does not
need to wait for kthread(), it can just return.  Instead kthread() itself
can wake up the caller of kthread_create().

Kill kthread_create_info->started, ->done is enough.  This improves the
scalability a bit and sijmplifies the code.

The only problem if kernel_thread() fails, in that case create_kthread()
must do complete(&create->done).

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: Rusty Russell <rusty@rustcorp.com.au>
Cc: Vitaliy Gusev <vgusev@openvz.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 7 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 7fa44133352..bc5d1f0b25a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -27,7 +27,6 @@ struct kthread_create_info
         /* Information passed to kthread() from kthreadd. */
         int (*threadfn)(void *data);
         void *data;
-        struct completion started;
 
         /* Result passed back to kthread_create() from kthreadd. */
         struct task_struct *result;
@@ -75,7 +74,7 @@ static int kthread(void *_create)
         /* OK, tell user we're spawned, wait for stop or wakeup */
         __set_current_state(TASK_UNINTERRUPTIBLE);
         create->result = current;
-        complete(&create->started);
+        complete(&create->done);
         schedule();
 
         if (!kthread_should_stop())
@@ -95,11 +94,10 @@ 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
-                wait_for_completion(&create->started);
-        complete(&create->done);
+                complete(&create->done);
+        }
 }
 
 /**
@@ -130,7 +128,6 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
 
         create.threadfn = threadfn;
         create.data = data;
-        init_completion(&create.started);
         init_completion(&create.done);
 
         spin_lock(&kthread_create_lock);