Re: 2.6.12-git8 Voluntary preempt hangs at boot

[Ingo Molnar <mingo@elte.hu>]

* Ash Milsted <thatistosayiseenem@gawab.com> wrote:

> Yes, this solves the problem. Cheers.

thanks! Andrew, Linus, would be nice to commit this one:

--------
Subject: sched-tweak-idle-thread-setup-semantics.patch
From: Ingo Molnar <mingo@elte.hu>

This patch tweaks idle thread setup semantics a bit: instead of setting
NEED_RESCHED in init_idle(), we do an explicit schedule() before calling
into cpu_idle().

This patch, while having no negative side-effects, enables wider use of
cond_resched()s.  (which might happen in the stock kernel too, but it's
particulary important for voluntary-preempt)

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

 init/main.c    |    7 +++++++
 kernel/sched.c |    9 ++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff -puN init/main.c~sched-tweak-idle-thread-setup-semantics init/main.c
--- 25/init/main.c~sched-tweak-idle-thread-setup-semantics	2005-06-25 01:17:13.000000000 -0700
+++ 25-akpm/init/main.c	2005-06-25 01:17:13.000000000 -0700
@@ -383,6 +383,13 @@ static void noinline rest_init(void)
 	numa_default_policy();
 	unlock_kernel();
 	preempt_enable_no_resched();
+
+	/*
+	 * The boot idle thread must execute schedule()
+	 * at least one to get things moving:
+	 */
+	schedule();
+
 	cpu_idle();
 } 
 
diff -puN kernel/sched.c~sched-tweak-idle-thread-setup-semantics kernel/sched.c
--- 25/kernel/sched.c~sched-tweak-idle-thread-setup-semantics	2005-06-25 01:17:13.000000000 -0700
+++ 25-akpm/kernel/sched.c	2005-06-25 01:17:13.000000000 -0700
@@ -4178,6 +4178,14 @@ void show_state(void)
 	read_unlock(&tasklist_lock);
 }
 
+/**
+ * init_idle - set up an idle thread for a given CPU
+ * @idle: task in question
+ * @cpu: cpu the idle task belongs to
+ *
+ * NOTE: this function does not set the idle thread's NEED_RESCHED
+ * flag, to make booting more robust.
+ */
 void __devinit init_idle(task_t *idle, int cpu)
 {
 	runqueue_t *rq = cpu_rq(cpu);
@@ -4195,7 +4203,6 @@ void __devinit init_idle(task_t *idle, i
 #if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
 	idle->oncpu = 1;
 #endif
-	set_tsk_need_resched(idle);
 	spin_unlock_irqrestore(&rq->lock, flags);
 
 	/* Set the preempt count _outside_ the spinlocks! */
_