sched: Create more preempt_count accessors

We need a few special preempt_count accessors:
 - task_preempt_count() for when we're interested in the preemption
   count of another (non-running) task.
 - init_task_preempt_count() for properly initializing the preemption
   count.
 - init_idle_preempt_count() a special case of the above for the idle
   threads.

With these no generic code ever touches thread_info::preempt_count
anymore and architectures could choose to remove it.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-jf5swrio8l78j37d06fzmo4r@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 18 insertions, 5 deletions

diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index a1fc6590a743..8100b1ec1715 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -28,6 +28,20 @@ static __always_inline void preempt_count_set(int pc)
 }
 
 /*
+ * must be macros to avoid header recursion hell
+ */
+#define task_preempt_count(p) \
+        (task_thread_info(p)->preempt_count & ~PREEMPT_NEED_RESCHED)
+
+#define init_task_preempt_count(p) do { \
+        task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \
+} while (0)
+
+#define init_idle_preempt_count(p, cpu) do { \
+        task_thread_info(p)->preempt_count = PREEMPT_ENABLED; \
+} while (0)
+
+/*
  * We fold the NEED_RESCHED bit into the preempt count such that
  * preempt_enable() can decrement and test for needing to reschedule with a
  * single instruction.
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 2e7d9947a10d..613381bcde40 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -100,7 +100,7 @@ static inline long __trace_sched_switch_state(struct task_struct *p)
         /*
          * For all intents and purposes a preempted task is a running task.
          */
-        if (task_thread_info(p)->preempt_count & PREEMPT_ACTIVE)
+        if (task_preempt_count(p) & PREEMPT_ACTIVE)
                 state = TASK_RUNNING | TASK_STATE_MAX;
 #endif
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee61f5affd20..0ba4e4192390 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -983,7 +983,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
          * 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));
+                        !(task_preempt_count(p) & PREEMPT_ACTIVE));
 
 #ifdef CONFIG_LOCKDEP
         /*
@@ -1723,8 +1723,7 @@ void sched_fork(struct task_struct *p)
         p->on_cpu = 0;
 #endif
 #ifdef CONFIG_PREEMPT_COUNT
-        /* Want to start with kernel preemption disabled. */
-        task_thread_info(p)->preempt_count = PREEMPT_DISABLED;
+        init_task_preempt_count(p);
 #endif
 #ifdef CONFIG_SMP
         plist_node_init(&p->pushable_tasks, MAX_PRIO);
@@ -4217,7 +4216,7 @@ void init_idle(struct task_struct *idle, int cpu)
         raw_spin_unlock_irqrestore(&rq->lock, flags);
 
         /* Set the preempt count _outside_ the spinlocks! */
-        task_thread_info(idle)->preempt_count = PREEMPT_ENABLED;
+        init_idle_preempt_count(idle, cpu);
 
         /*
          * The idle tasks have their own, simple scheduling class: