[RFC][PATCH 4/5] sched: Create more preempt_count accessors

Peter Zijlstra
2013-08-14T13:41:11Z

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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-ko6tuved7x9y0t08qxhhnubz@git.kernel.org
---
include/asm-generic/preempt.h | 14 ++++++++++++++
include/trace/events/sched.h | 2 +-
kernel/sched/core.c | 7 +++----
3 files changed, 18 insertions(+), 5 deletions(-)

--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -17,4 +17,18 @@ static __always_inline int *preempt_coun
return &current_thread_info()->preempt_count;
}

+/*
+ * 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 = 1 | PREEMPT_NEED_RESCHED; \
+} while (0)
+
+#define init_idle_preempt_count(p, cpu) do { \
+ task_thread_info(p)->preempt_count = 0; \
+} while (0)
+
#endif /* __ASM_PREEMPT_H */
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -103,7 +103,7 @@ static inline long __trace_sched_switch_
/*
* 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

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -996,7 +996,7 @@ void set_task_cpu(struct task_struct *p,
* 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
/*
@@ -1737,8 +1737,7 @@ 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 = 1;
+ init_task_preempt_count(p);
#endif
#ifdef CONFIG_SMP
plist_node_init(&p->pushable_tasks, MAX_PRIO);
@@ -4225,7 +4224,7 @@ void init_idle(struct task_struct *idle,
raw_spin_unlock_irqrestore(&rq->lock, flags);

/* Set the preempt count _outside_ the spinlocks! */
- task_thread_info(idle)->preempt_count = 0;
+ init_idle_preempt_count(idle, cpu);

/*
* The idle tasks have their own, simple scheduling class: