path: root/sched-preempt-rt-support.patch

From f028827ac82420d6ef5d751562e3244f6dbac723 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:30:03 -0500
Subject: [PATCH] sched: preempt-rt support

commit 0a930ce98838ed0a03530fd4960eb3423c9b55bc in tip.

[PG: original in tip relocated __might_sleep; drop that chunk,
 also fold some sched changes buried in merge commits back here.
 Upstream merged the ttwu changes, but note with caution that
 they compare for equality, not just if TASK_WAKING bit is set.
 This preserves the bit test used in the original RT patch.]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 include/linux/hardirq.h |    7 +-
 include/linux/sched.h   |   49 ++++++++
 kernel/mutex.c          |    7 +-
 kernel/sched.c          |  297 ++++++++++++++++++++++++++++++++++++++---------
 kernel/sched_fair.c     |    6 +-
 kernel/sched_rt.c       |   54 ++++++++-
 lib/kernel_lock.c       |    1 -
 7 files changed, 361 insertions(+), 60 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 5d79504..cee2da4 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -92,6 +92,8 @@
  */
 #define in_nmi()	(preempt_count() & NMI_MASK)
 
+#define PREEMPT_INATOMIC_BASE 0
+
 /*
  * Are we running in atomic context?  WARNING: this macro cannot
  * always detect atomic context; in particular, it cannot know about
@@ -99,7 +101,8 @@
  * used in the general case to determine whether sleeping is possible.
  * Do not use in_atomic() in driver code.
  */
-#define in_atomic()		((preempt_count() & ~PREEMPT_ACTIVE) != 0)
+#define in_atomic()	\
+	((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_INATOMIC_BASE)
 
 #ifdef CONFIG_PREEMPT
 # define PREEMPT_CHECK_OFFSET 1
@@ -112,7 +115,7 @@
  * (used by the scheduler)
  */
 #define in_atomic_preempt_off() \
-		((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
+	((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
 
 #ifdef CONFIG_PREEMPT
 # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 379fec4..5c73160 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -102,6 +102,17 @@ struct fs_struct;
 struct bts_context;
 struct perf_event_context;
 
+#ifdef CONFIG_PREEMPT
+extern int kernel_preemption;
+#else
+# define kernel_preemption 0
+#endif
+#ifdef CONFIG_PREEMPT_VOLUNTARY
+extern int voluntary_preemption;
+#else
+# define voluntary_preemption 0
+#endif
+
 #ifdef CONFIG_PREEMPT_SOFTIRQS
 extern int softirq_preemption;
 #else
@@ -235,6 +246,28 @@ extern char ___assert_task_state[1 - 2*!!(
 #define set_task_state(tsk, state_value)		\
 	set_mb((tsk)->state, (state_value))
 
+// #define PREEMPT_DIRECT
+
+#ifdef CONFIG_X86_LOCAL_APIC
+extern void nmi_show_all_regs(void);
+#else
+# define nmi_show_all_regs() do { } while (0)
+#endif
+
+#include <linux/smp.h>
+#include <linux/sem.h>
+#include <linux/signal.h>
+#include <linux/securebits.h>
+#include <linux/fs_struct.h>
+#include <linux/compiler.h>
+#include <linux/completion.h>
+#include <linux/pid.h>
+#include <linux/percpu.h>
+#include <linux/topology.h>
+#include <linux/seccomp.h>
+
+struct exec_domain;
+
 /*
  * set_current_state() includes a barrier so that the write of current->state
  * is correctly serialised wrt the caller's subsequent test of whether to
@@ -371,6 +404,11 @@ extern signed long schedule_timeout_killable(signed long timeout);
 extern signed long schedule_timeout_uninterruptible(signed long timeout);
 asmlinkage void schedule(void);
 extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner);
+/*
+ * This one can be called with interrupts disabled, only
+ * to be used by lowlevel arch code!
+ */
+asmlinkage void __sched __schedule(void);
 
 struct nsproxy;
 struct user_namespace;
@@ -1712,6 +1750,15 @@ extern struct pid *cad_pid;
 extern void free_task(struct task_struct *tsk);
 #define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0)
 
+#ifdef CONFIG_PREEMPT_RT
+extern void __put_task_struct_cb(struct rcu_head *rhp);
+
+static inline void put_task_struct(struct task_struct *t)
+{
+	if (atomic_dec_and_test(&t->usage))
+		call_rcu(&t->rcu, __put_task_struct_cb);
+}
+#else
 extern void __put_task_struct(struct task_struct *t);
 
 static inline void put_task_struct(struct task_struct *t)
@@ -1719,6 +1766,7 @@ static inline void put_task_struct(struct task_struct *t)
 	if (atomic_dec_and_test(&t->usage))
 		__put_task_struct(t);
 }
+#endif
 
 extern void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st);
 extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st);
@@ -1973,6 +2021,7 @@ extern struct task_struct *curr_task(int cpu);
 extern void set_curr_task(int cpu, struct task_struct *p);
 
 void yield(void);
+void __yield(void);
 
 /*
  * The default (Linux) execution domain.
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 90ed15f..432607a 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -249,8 +249,13 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 
 		/* didnt get the lock, go to sleep: */
 		spin_unlock_mutex(&lock->wait_lock, flags);
-		preempt_enable_and_schedule();
+
+		local_irq_disable();
+		__preempt_enable_no_resched();
+		__schedule();
 		preempt_disable();
+		local_irq_enable();
+
 		spin_lock_mutex(&lock->wait_lock, flags);
 	}
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 094cb0c..c41e84c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4,6 +4,7 @@
  *  Kernel scheduler and related syscalls
  *
  *  Copyright (C) 1991-2002  Linus Torvalds
+ *  Copyright (C) 2004 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *
  *  1996-12-23  Modified by Dave Grothe to fix bugs in semaphores and
  *		make semaphores SMP safe
@@ -16,6 +17,7 @@
  *		by Davide Libenzi, preemptible kernel bits by Robert Love.
  *  2003-09-03	Interactivity tuning by Con Kolivas.
  *  2004-04-02	Scheduler domains code by Nick Piggin
+ *  2004-10-13  Real-Time Preemption support by Ingo Molnar
  *  2007-04-15  Work begun on replacing all interactivity tuning with a
  *              fair scheduling design by Con Kolivas.
  *  2007-05-05  Load balancing (smp-nice) and other improvements
@@ -61,6 +63,7 @@
 #include <linux/sysctl.h>
 #include <linux/syscalls.h>
 #include <linux/times.h>
+#include <linux/kallsyms.h>
 #include <linux/tsacct_kern.h>
 #include <linux/kprobes.h>
 #include <linux/delayacct.h>
@@ -107,6 +110,20 @@
 #define NICE_0_LOAD		SCHED_LOAD_SCALE
 #define NICE_0_SHIFT		SCHED_LOAD_SHIFT
 
+#if (BITS_PER_LONG < 64)
+#define JIFFIES_TO_NS64(TIME) \
+	((unsigned long long)(TIME) * ((unsigned long) (1000000000 / HZ)))
+
+#define NS64_TO_JIFFIES(TIME) \
+	((((unsigned long long)((TIME)) >> BITS_PER_LONG) * \
+	(1 + NS_TO_JIFFIES(~0UL))) + NS_TO_JIFFIES((unsigned long)(TIME)))
+#else /* BITS_PER_LONG < 64 */
+
+#define NS64_TO_JIFFIES(TIME) NS_TO_JIFFIES(TIME)
+#define JIFFIES_TO_NS64(TIME) JIFFIES_TO_NS(TIME)
+
+#endif /* BITS_PER_LONG < 64 */
+
 /*
  * These are the 'tuning knobs' of the scheduler:
  *
@@ -132,6 +149,9 @@ static inline int task_has_rt_policy(struct task_struct *p)
 	return rt_policy(p->policy);
 }
 
+#define TASK_PREEMPTS_CURR(p, rq) \
+	((p)->prio < (rq)->curr->prio)
+
 /*
  * This is the priority-queue data structure of the RT scheduling class:
  */
@@ -358,6 +378,7 @@ static inline struct task_group *task_group(struct task_struct *p)
 struct cfs_rq {
 	struct load_weight load;
 	unsigned long nr_running;
+	unsigned long nr_enqueued;
 
 	u64 exec_clock;
 	u64 min_vruntime;
@@ -435,6 +456,7 @@ struct rt_rq {
 	int overloaded;
 	struct plist_head pushable_tasks;
 #endif
+	unsigned long rt_nr_uninterruptible;
 	int rt_throttled;
 	u64 rt_time;
 	u64 rt_runtime;
@@ -529,6 +551,8 @@ struct rq {
 	 */
 	unsigned long nr_uninterruptible;
 
+	unsigned long switch_timestamp;
+	unsigned long slice_avg;
 	struct task_struct *curr, *idle;
 	unsigned long next_balance;
 	struct mm_struct *prev_mm;
@@ -593,6 +617,13 @@ struct rq {
 
 	/* BKL stats */
 	unsigned int bkl_count;
+
+	/* RT-overload stats: */
+	unsigned long rto_schedule;
+	unsigned long rto_schedule_tail;
+	unsigned long rto_wakeup;
+	unsigned long rto_pulled;
+	unsigned long rto_pushed;
 #endif
 };
 
@@ -836,11 +867,23 @@ static inline u64 global_rt_runtime(void)
 	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
 }
 
+/*
+ * We really dont want to do anything complex within switch_to()
+ * on PREEMPT_RT - this check enforces this.
+ */
+#ifdef prepare_arch_switch
+# ifdef CONFIG_PREEMPT_RT
+#   error FIXME
+# else
+#  define _finish_arch_switch finish_arch_switch
+# endif
+#endif
+
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)	do { } while (0)
 #endif
 #ifndef finish_arch_switch
-# define finish_arch_switch(prev)	do { } while (0)
+# define _finish_arch_switch(prev)	do { } while (0)
 #endif
 
 static inline int task_current(struct rq *rq, struct task_struct *p)
@@ -871,7 +914,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 	 */
 	spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
 
-	raw_spin_unlock_irq(&rq->lock);
+	raw_spin_unlock(&rq->lock);
 }
 
 #else /* __ARCH_WANT_UNLOCKED_CTXSW */
@@ -912,8 +955,8 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 	smp_wmb();
 	prev->oncpu = 0;
 #endif
-#ifndef __ARCH_WANT_INTERRUPTS_ON_CTXSW
-	local_irq_enable();
+#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
+	local_irq_disable();
 #endif
 }
 #endif /* __ARCH_WANT_UNLOCKED_CTXSW */
@@ -928,7 +971,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
  */
 static inline int task_is_waking(struct task_struct *p)
 {
-	return unlikely((p->state == TASK_WAKING) && !(p->flags & PF_STARTING));
+	return unlikely((p->state & TASK_WAKING) && !(p->flags & PF_STARTING));
 }
 
 /*
@@ -2040,13 +2083,20 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
 
 void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 {
-#ifdef CONFIG_SCHED_DEBUG
+#if defined(CONFIG_SCHED_DEBUG)
 	/*
 	 * We should never call set_task_cpu() on a blocked task,
 	 * ttwu() will sort out the placement.
 	 */
-	WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
-			!(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));
+	if (p->state != TASK_RUNNING &&
+	    !(p->state & TASK_WAKING) &&
+	    !(p->state & TASK_RUNNING_MUTEX) &&
+	    !(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE)) {
+		printk(KERN_ERR "%d %s %lx %lx\n", p->pid, p->comm,
+		       (unsigned long) p->state,
+		       (unsigned long) preempt_count());
+		WARN_ON(1);
+	}
 #endif
 
 	trace_sched_migrate_task(p, new_cpu);
@@ -2373,8 +2423,7 @@ int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags)
  *
  * returns failure only if the task is already active.
  */
-static int
-try_to_wake_up(struct task_struct *p, unsigned int state,
+static int try_to_wake_up(struct task_struct *p, unsigned int state,
 			  int wake_flags, int mutex)
 {
 	int cpu, orig_cpu, this_cpu, success = 0;
@@ -2405,12 +2454,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state,
 	/*
 	 * In order to handle concurrent wakeups and release the rq->lock
 	 * we put the task in TASK_WAKING state.
-	 *
-	 * First fix up the nr_uninterruptible count:
 	 */
-	if (task_contributes_to_load(p))
-		rq->nr_uninterruptible--;
-	p->state = TASK_WAKING;
+	p->state |= TASK_WAKING;
 
 	if (p->sched_class->task_waking)
 		p->sched_class->task_waking(rq, p);
@@ -2438,7 +2483,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state,
 	 * cpu we just moved it to.
 	 */
 	WARN_ON(task_cpu(p) != cpu);
-	WARN_ON(p->state != TASK_WAKING);
+	WARN_ON(!(p->state & TASK_WAKING));
 
 #ifdef CONFIG_SCHEDSTATS
 	schedstat_inc(rq, ttwu_count);
@@ -2497,10 +2542,12 @@ out_running:
 	 * here. The waiter is serialized by the mutex lock and nobody
 	 * else can fiddle with p->state as we hold rq lock.
 	 */
+	p->state &= ~TASK_WAKING;
 	if (mutex)
 		p->state |= TASK_RUNNING_MUTEX;
 	else
 		p->state = TASK_RUNNING;
+
 #ifdef CONFIG_SMP
 	if (p->sched_class->task_woken)
 		p->sched_class->task_woken(rq, p);
@@ -2627,7 +2674,7 @@ static void __sched_fork(struct task_struct *p)
  */
 void sched_fork(struct task_struct *p, int clone_flags)
 {
-	int cpu = get_cpu();
+	int cpu;
 
 	__sched_fork(p);
 	/*
@@ -2667,11 +2714,19 @@ void sched_fork(struct task_struct *p, int clone_flags)
 	if (!rt_prio(p->prio))
 		p->sched_class = &fair_sched_class;
 
+	/*
+	 * task_fork() and set_task_cpu() must be called with
+	 * preemption disabled
+	 */
+	cpu = get_cpu();
+
 	if (p->sched_class->task_fork)
 		p->sched_class->task_fork(p);
 
 	set_task_cpu(p, cpu);
 
+	put_cpu();
+
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 	if (likely(sched_info_on()))
 		memset(&p->sched_info, 0, sizeof(p->sched_info));
@@ -2684,8 +2739,6 @@ void sched_fork(struct task_struct *p, int clone_flags)
 	task_thread_info(p)->preempt_count = 1;
 #endif
 	plist_node_init(&p->pushable_tasks, MAX_PRIO);
-
-	put_cpu();
 }
 
 /*
@@ -2851,7 +2904,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
 	 *		Manfred Spraul <manfred@colorfullife.com>
 	 */
 	prev_state = prev->state;
-	finish_arch_switch(prev);
+	_finish_arch_switch(prev);
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
 	local_irq_disable();
 #endif /* __ARCH_WANT_INTERRUPTS_ON_CTXSW */
@@ -2917,8 +2970,10 @@ static inline void post_schedule(struct rq *rq)
 asmlinkage void schedule_tail(struct task_struct *prev)
 	__releases(rq->lock)
 {
-	struct rq *rq = this_rq();
+	struct rq *rq;
 
+	preempt_disable();
+	rq = this_rq();
 	finish_task_switch(rq, prev);
 
 	/*
@@ -2927,9 +2982,14 @@ asmlinkage void schedule_tail(struct task_struct *prev)
 	 */
 	post_schedule(rq);
 
+	__preempt_enable_no_resched();
+	local_irq_enable();
+
 #ifdef __ARCH_WANT_UNLOCKED_CTXSW
 	/* In this case, finish_task_switch does not reenable preemption */
 	preempt_enable();
+#else
+	preempt_check_resched();
 #endif
 	if (current->set_child_tid)
 		put_user(task_pid_vnr(current), current->set_child_tid);
@@ -2977,6 +3037,11 @@ context_switch(struct rq *rq, struct task_struct *prev,
 	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
 #endif
 
+#ifdef CURRENT_PTR
+	barrier();
+	*current_ptr = next;
+	*current_ti_ptr = next->thread_info;
+#endif
 	/* Here we just switch the register state and the stack. */
 	switch_to(prev, next, prev);
 
@@ -3023,6 +3088,11 @@ unsigned long nr_uninterruptible(void)
 	return sum;
 }
 
+unsigned long nr_uninterruptible_cpu(int cpu)
+{
+	return cpu_rq(cpu)->nr_uninterruptible;
+}
+
 unsigned long long nr_context_switches(void)
 {
 	int i;
@@ -3559,6 +3629,8 @@ void scheduler_tick(void)
 
 	sched_clock_tick();
 
+	BUG_ON(!irqs_disabled());
+
 	raw_spin_lock(&rq->lock);
 	update_rq_clock(rq);
 	update_cpu_load(rq);
@@ -3652,8 +3724,8 @@ static noinline void __schedule_bug(struct task_struct *prev)
 {
 	struct pt_regs *regs = get_irq_regs();
 
-	printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
-		prev->comm, prev->pid, preempt_count());
+	printk(KERN_ERR "BUG: scheduling while atomic: %s/0x%08x/%d, CPU#%d\n",
+	       prev->comm, preempt_count(), prev->pid, smp_processor_id());
 
 	debug_show_held_locks(prev);
 	print_modules();
@@ -3671,12 +3743,14 @@ static noinline void __schedule_bug(struct task_struct *prev)
  */
 static inline void schedule_debug(struct task_struct *prev)
 {
+//	WARN_ON(system_state == SYSTEM_BOOTING);
+
 	/*
 	 * Test if we are atomic. Since do_exit() needs to call into
 	 * schedule() atomically, we ignore that path for now.
 	 * Otherwise, whine if we are scheduling when we should not be.
 	 */
-	if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
+	if (unlikely(in_atomic() && !prev->exit_state))
 		__schedule_bug(prev);
 
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
@@ -3761,10 +3835,11 @@ asmlinkage void __sched __schedule(void)
 	switch_count = &prev->nivcsw;
 
 	release_kernel_lock(prev);
-need_resched_nonpreemptible:
 
 	schedule_debug(prev);
 
+	preempt_disable();
+
 	if (sched_feat(HRTICK))
 		hrtick_clear(rq);
 
@@ -3804,30 +3879,29 @@ need_resched_nonpreemptible:
 		 */
 		cpu = smp_processor_id();
 		rq = cpu_rq(cpu);
-	} else
-		raw_spin_unlock_irq(&rq->lock);
+		__preempt_enable_no_resched();
+	} else {
+		__preempt_enable_no_resched();
+		raw_spin_unlock(&rq->lock);
+	}
 
 	post_schedule(rq);
 
-	if (unlikely(reacquire_kernel_lock(current) < 0)) {
-		prev = rq->curr;
-		switch_count = &prev->nivcsw;
-		goto need_resched_nonpreemptible;
-	}
+	reacquire_kernel_lock(current);
 }
 
 asmlinkage void __sched schedule(void)
 {
 need_resched:
-	preempt_disable();
+	local_irq_disable();
 	__schedule();
-	__preempt_enable_no_resched();
+	local_irq_enable();
 	if (need_resched())
 		goto need_resched;
 }
 EXPORT_SYMBOL(schedule);
 
-#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+#if defined(CONFIG_MUTEX_SPIN_ON_OWNER) && !defined(CONFIG_PREEMPT_RT)
 /*
  * Look out! "owner" is an entirely speculative pointer
  * access and not reliable.
@@ -3889,6 +3963,35 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
 #endif
 
 #ifdef CONFIG_PREEMPT
+
+/*
+ * Global flag to turn preemption off on a CONFIG_PREEMPT kernel:
+ */
+int kernel_preemption = 1;
+
+static int __init preempt_setup (char *str)
+{
+	if (!strncmp(str, "off", 3)) {
+		if (kernel_preemption) {
+			printk(KERN_INFO "turning off kernel preemption!\n");
+			kernel_preemption = 0;
+		}
+		return 1;
+	}
+	if (!strncmp(str, "on", 2)) {
+		if (!kernel_preemption) {
+			printk(KERN_INFO "turning on kernel preemption!\n");
+			kernel_preemption = 1;
+		}
+		return 1;
+	}
+	get_option(&str, &kernel_preemption);
+
+	return 1;
+}
+
+__setup("preempt=", preempt_setup);
+
 /*
  * this is the entry point to schedule() from in-kernel preemption
  * off of preempt_enable. Kernel preemptions off return from interrupt
@@ -3900,6 +4003,8 @@ asmlinkage void __sched preempt_schedule(void)
 	struct task_struct *task = current;
 	int saved_lock_depth;
 
+	if (!kernel_preemption)
+		return;
 	/*
 	 * If there is a non-zero preempt_count or interrupts are disabled,
 	 * we do not want to preempt the current task. Just return..
@@ -3908,6 +4013,7 @@ asmlinkage void __sched preempt_schedule(void)
 		return;
 
 	do {
+		local_irq_disable();
 		add_preempt_count(PREEMPT_ACTIVE);
 
 		/*
@@ -3917,10 +4023,13 @@ asmlinkage void __sched preempt_schedule(void)
 		 */
 		saved_lock_depth = task->lock_depth;
 		task->lock_depth = -1;
-		schedule();
+		__schedule();
 		task->lock_depth = saved_lock_depth;
+
 		sub_preempt_count(PREEMPT_ACTIVE);
 
+		local_irq_enable();
+
 		/*
 		 * Check again in case we missed a preemption opportunity
 		 * between schedule and now.
@@ -3931,10 +4040,10 @@ asmlinkage void __sched preempt_schedule(void)
 EXPORT_SYMBOL(preempt_schedule);
 
 /*
- * this is the entry point to schedule() from kernel preemption
- * off of irq context.
- * Note, that this is called and return with irqs disabled. This will
- * protect us against recursive calling from irq.
+ * this is is the entry point for the IRQ return path. Called with
+ * interrupts disabled.  To avoid infinite irq-entry recursion problems
+ * with fast-paced IRQ sources we do all of this carefully to never
+ * enable interrupts again.
  */
 asmlinkage void __sched preempt_schedule_irq(void)
 {
@@ -3942,10 +4051,17 @@ asmlinkage void __sched preempt_schedule_irq(void)
 	struct task_struct *task = current;
 	int saved_lock_depth;
 
-	/* Catch callers which need to be fixed */
-	WARN_ON_ONCE(ti->preempt_count || !irqs_disabled());
+	if (!kernel_preemption)
+		return;
+	/*
+	 * If there is a non-zero preempt_count then just return.
+	 * (interrupts are disabled)
+	 */
+	if (unlikely(ti->preempt_count))
+		return;
 
 	do {
+		local_irq_disable();
 		add_preempt_count(PREEMPT_ACTIVE);
 
 		/*
@@ -3955,9 +4071,8 @@ asmlinkage void __sched preempt_schedule_irq(void)
 		 */
 		saved_lock_depth = task->lock_depth;
 		task->lock_depth = -1;
-		local_irq_enable();
-		schedule();
-		local_irq_disable();
+		__schedule();
+
 		task->lock_depth = saved_lock_depth;
 		sub_preempt_count(PREEMPT_ACTIVE);
 
@@ -4382,6 +4497,7 @@ void task_setprio(struct task_struct *p, int prio)
 
 		check_class_changed(rq, p, prev_class, oldprio, running);
 	}
+
 	task_rq_unlock(rq, &flags);
 }
 
@@ -5034,6 +5150,7 @@ SYSCALL_DEFINE0(sched_yield)
 	__release(rq->lock);
 	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
 	do_raw_spin_unlock(&rq->lock);
+	local_irq_enable();
 
 	preempt_enable_and_schedule();
 
@@ -5047,9 +5164,18 @@ static inline int should_resched(void)
 
 static void __cond_resched(void)
 {
-	add_preempt_count(PREEMPT_ACTIVE);
-	schedule();
-	sub_preempt_count(PREEMPT_ACTIVE);
+	do {
+		add_preempt_count(PREEMPT_ACTIVE);
+		schedule();
+		sub_preempt_count(PREEMPT_ACTIVE);
+
+		/*
+		 * Check again in case we missed a preemption opportunity
+		 * between schedule and now.
+		 */
+		barrier();
+
+	} while (need_resched());
 }
 
 int __sched _cond_resched(void)
@@ -5095,8 +5221,11 @@ EXPORT_SYMBOL(__cond_resched_lock);
  */
 int __sched __cond_resched_softirq(void)
 {
+#ifndef CONFIG_PREEMPT_SOFTIRQS
 	WARN_ON_ONCE(!in_softirq());
-
+	if (!in_softirq())
+		return 0;
+#endif
 	if (should_resched()) {
 		local_bh_enable();
 		__cond_resched();
@@ -5126,17 +5255,56 @@ int __sched cond_resched_softirq_context(void)
 }
 EXPORT_SYMBOL(cond_resched_softirq_context);
 
+#ifdef CONFIG_PREEMPT_VOLUNTARY
+int voluntary_preemption = 1;
+EXPORT_SYMBOL(voluntary_preemption);
+
+static int __init voluntary_preempt_setup (char *str)
+{
+	if (!strncmp(str, "off", 3))
+		voluntary_preemption = 0;
+	else
+		get_option(&str, &voluntary_preemption);
+	if (!voluntary_preemption)
+		printk("turning off voluntary preemption!\n");
+
+	return 1;
+}
+
+__setup("voluntary-preempt=", voluntary_preempt_setup);
+
+#endif
+
 /**
  * yield - yield the current processor to other threads.
  *
  * This is a shortcut for kernel-space yielding - it marks the
  * thread runnable and calls sys_sched_yield().
  */
-void __sched yield(void)
+void __sched __yield(void)
 {
 	set_current_state(TASK_RUNNING);
 	sys_sched_yield();
 }
+
+void __sched yield(void)
+{
+	static int once = 1;
+
+	/*
+	 * it's a bug to rely on yield() with RT priorities. We print
+	 * the first occurance after bootup ... this will still give
+	 * us an idea about the scope of the problem, without spamming
+	 * the syslog:
+	 */
+	if (once && rt_task(current)) {
+		once = 0;
+		printk(KERN_ERR "BUG: %s:%d RT task yield()-ing!\n",
+			current->comm, current->pid);
+		dump_stack();
+	}
+	__yield();
+}
 EXPORT_SYMBOL(yield);
 
 /*
@@ -5300,6 +5468,7 @@ void sched_show_task(struct task_struct *p)
 void show_state_filter(unsigned long state_filter)
 {
 	struct task_struct *g, *p;
+	int do_unlock = 1;
 
 #if BITS_PER_LONG == 32
 	printk(KERN_INFO
@@ -5308,7 +5477,16 @@ void show_state_filter(unsigned long state_filter)
 	printk(KERN_INFO
 		"  task                        PC stack   pid father\n");
 #endif
+#ifdef CONFIG_PREEMPT_RT
+	if (!read_trylock(&tasklist_lock)) {
+		printk("hm, tasklist_lock write-locked.\n");
+		printk("ignoring ...\n");
+		do_unlock = 0;
+	}
+#else
 	read_lock(&tasklist_lock);
+#endif
+
 	do_each_thread(g, p) {
 		/*
 		 * reset the NMI-timeout, listing all files on a slow
@@ -5324,7 +5502,8 @@ void show_state_filter(unsigned long state_filter)
 #ifdef CONFIG_SCHED_DEBUG
 	sysrq_sched_debug_show();
 #endif
-	read_unlock(&tasklist_lock);
+	if (do_unlock)
+		read_unlock(&tasklist_lock);
 	/*
 	 * Only show locks if all tasks are dumped:
 	 */
@@ -5432,7 +5611,7 @@ static inline void sched_init_granularity(void)
 	update_sysctl();
 }
 
-#if defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT_RT)
+#ifdef CONFIG_SMP
 /*
  * This is how migration works:
  *
@@ -5522,11 +5701,18 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
 static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
 {
 	struct rq *rq_dest, *rq_src;
+	unsigned long flags;
 	int ret = 0;
 
 	if (unlikely(!cpu_active(dest_cpu)))
 		return ret;
 
+	 /*
+	  * PREEMPT_RT: this relies on write_lock_irq(&tasklist_lock)
+	  * disabling interrupts - which on PREEMPT_RT does not do:
+	  */
+	local_irq_save(flags);
+
 	rq_src = cpu_rq(src_cpu);
 	rq_dest = cpu_rq(dest_cpu);
 
@@ -5552,6 +5738,8 @@ done:
 	ret = 1;
 fail:
 	double_rq_unlock(rq_src, rq_dest);
+	local_irq_restore(flags);
+
 	return ret;
 }
 
@@ -7925,6 +8113,9 @@ void __init sched_init(void)
 	atomic_inc(&init_mm.mm_count);
 	enter_lazy_tlb(&init_mm, current);
 
+#ifdef CONFIG_PREEMPT_RT
+	printk("Real-Time Preemption Support (C) 2004-2007 Ingo Molnar\n");
+#endif
 	/*
 	 * Make us the idle thread. Technically, schedule() should not be
 	 * called from this thread, however somewhere below it might be,
@@ -7957,7 +8148,7 @@ void __init sched_init(void)
 	scheduler_running = 1;
 }
 
-#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
+#if defined(CONFIG_DEBUG_SPINLOCK_SLEEP) || defined(CONFIG_DEBUG_PREEMPT)
 static inline int preempt_count_equals(int preempt_offset)
 {
 	int nested = (preempt_count() & ~PREEMPT_ACTIVE) + rcu_preempt_depth();
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5a5ea2c..b944efc 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -360,6 +360,8 @@ static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 	rb_link_node(&se->run_node, parent, link);
 	rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
+
+	cfs_rq->nr_enqueued++;
 }
 
 static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -372,6 +374,8 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	}
 
 	rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
+
+	cfs_rq->nr_enqueued--;
 }
 
 static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
@@ -1062,7 +1066,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup, bool head)
 
 	if (wakeup)
 		flags |= ENQUEUE_WAKEUP;
-	if (p->state == TASK_WAKING)
+	if (p->state & TASK_WAKING)
 		flags |= ENQUEUE_MIGRATE;
 
 	for_each_sched_entity(se) {
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index b5b920a..1996902 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -884,6 +884,48 @@ static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
 	}
 }
 
+static inline void incr_rt_nr_uninterruptible(struct task_struct *p,
+					      struct rq *rq)
+{
+	rq->rt.rt_nr_uninterruptible++;
+}
+
+static inline void decr_rt_nr_uninterruptible(struct task_struct *p,
+					      struct rq *rq)
+{
+	rq->rt.rt_nr_uninterruptible--;
+}
+
+unsigned long rt_nr_running(void)
+{
+	unsigned long i, sum = 0;
+
+	for_each_online_cpu(i)
+		sum += cpu_rq(i)->rt.rt_nr_running;
+
+	return sum;
+}
+
+unsigned long rt_nr_running_cpu(int cpu)
+{
+	return cpu_rq(cpu)->rt.rt_nr_running;
+}
+
+unsigned long rt_nr_uninterruptible(void)
+{
+	unsigned long i, sum = 0;
+
+	for_each_online_cpu(i)
+		sum += cpu_rq(i)->rt.rt_nr_uninterruptible;
+
+	return sum;
+}
+
+unsigned long rt_nr_uninterruptible_cpu(int cpu)
+{
+	return cpu_rq(cpu)->rt.rt_nr_uninterruptible;
+}
+
 /*
  * Adding/removing a task to/from a priority array:
  */
@@ -897,6 +939,9 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup, bool head)
 
 	enqueue_rt_entity(rt_se, head);
 
+	if (p->state == TASK_UNINTERRUPTIBLE)
+		decr_rt_nr_uninterruptible(p, rq);
+
 	if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
 		enqueue_pushable_task(rq, p);
 }
@@ -906,6 +951,10 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
 	struct sched_rt_entity *rt_se = &p->rt;
 
 	update_curr_rt(rq);
+
+	if (p->state == TASK_UNINTERRUPTIBLE)
+		incr_rt_nr_uninterruptible(p, rq);
+
 	dequeue_rt_entity(rt_se);
 
 	dequeue_pushable_task(rq, p);
@@ -1474,8 +1523,10 @@ static int pull_rt_task(struct rq *this_rq)
 static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
 {
 	/* Try to pull RT tasks here if we lower this rq's prio */
-	if (unlikely(rt_task(prev)) && rq->rt.highest_prio.curr > prev->prio)
+	if (unlikely(rt_task(prev)) && rq->rt.highest_prio.curr > prev->prio) {
 		pull_rt_task(rq);
+		schedstat_inc(rq, rto_schedule);
+	}
 }
 
 static void post_schedule_rt(struct rq *rq)
@@ -1525,7 +1576,6 @@ static void set_cpus_allowed_rt(struct task_struct *p,
 			 */
 			if (weight > 1)
 				enqueue_pushable_task(rq, p);
-
 		}
 
 		if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) {
diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c
index e495acf..79f9fac 100644
--- a/lib/kernel_lock.c
+++ b/lib/kernel_lock.c
@@ -50,7 +50,6 @@ int __lockfunc __reacquire_kernel_lock(void)
 
 	down(&kernel_sem);
 
-	preempt_disable();
 	local_irq_disable();
 	current->lock_depth = saved_lock_depth;
 
-- 
1.7.0.4