sched/rt: Document scheduler related skip-resched-check sites

Create a distinction between scheduler related preempt_enable_no_resched()
calls and the nearly one hundred other places in the kernel that do not
want to reschedule, for one reason or another.

This distinction matters for -rt, where the scheduler and the non-scheduler
preempt models (and checks) are different. For upstream it's purely
documentational.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-gs88fvx2mdv5psnzxnv575ke@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

5 files changed, 11 insertions, 8 deletions

diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index 65035141552b..c97fc60c790c 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -102,7 +102,7 @@ void cpu_idle(void)
                 rcu_idle_exit();
                 tick_nohz_idle_exit();
                 if (cpu_should_die()) {
-                        preempt_enable_no_resched();
+                        sched_preempt_enable_no_resched();
                         cpu_die();
                 }
                 schedule_preempt_disabled();
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index ab9a29268213..06b5b5fc20c7 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -106,7 +106,7 @@ void cpu_idle(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
                 if (cpu_is_offline(cpu)) {
-                        preempt_enable_no_resched();
+                        sched_preempt_enable_no_resched();
                         cpu_play_dead();
                 }
 #endif
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 58969b2a8a82..5a710b9c578e 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -48,12 +48,14 @@ do { \
         barrier(); \
 } while (0)
 
-#define preempt_enable_no_resched() \
+#define sched_preempt_enable_no_resched() \
 do { \
         barrier(); \
         dec_preempt_count(); \
 } while (0)
 
+#define preempt_enable_no_resched()     sched_preempt_enable_no_resched()
+
 #define preempt_enable() \
 do { \
         preempt_enable_no_resched(); \
@@ -92,6 +94,7 @@ do { \
 #else /* !CONFIG_PREEMPT_COUNT */
 
 #define preempt_disable()               do { } while (0)
+#define sched_preempt_enable_no_resched()       do { } while (0)
 #define preempt_enable_no_resched()     do { } while (0)
 #define preempt_enable()                do { } while (0)
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 73022395c00e..643cc37fcb23 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3220,7 +3220,7 @@ need_resched:
 
         post_schedule(rq);
 
-        preempt_enable_no_resched();
+        sched_preempt_enable_no_resched();
         if (need_resched())
                 goto need_resched;
 }
@@ -3253,7 +3253,7 @@ EXPORT_SYMBOL(schedule);
  */
 void __sched schedule_preempt_disabled(void)
 {
-        preempt_enable_no_resched();
+        sched_preempt_enable_no_resched();
         schedule();
         preempt_disable();
 }
@@ -4486,7 +4486,7 @@ SYSCALL_DEFINE0(sched_yield)
         __release(rq->lock);
         spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
         do_raw_spin_unlock(&rq->lock);
-        preempt_enable_no_resched();
+        sched_preempt_enable_no_resched();
 
         schedule();
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 79b524767a24..f268369ebe1f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -353,7 +353,7 @@ void irq_exit(void)
                 tick_nohz_irq_exit();
 #endif
         rcu_irq_exit();
-        preempt_enable_no_resched();
+        sched_preempt_enable_no_resched();
 }
 
 /*
@@ -759,7 +759,7 @@ static int run_ksoftirqd(void * __bind_cpu)
                         if (local_softirq_pending())
                                 __do_softirq();
                         local_irq_enable();
-                        preempt_enable_no_resched();
+                        sched_preempt_enable_no_resched();
                         cond_resched();
                         preempt_disable();
                         rcu_note_context_switch((long)__bind_cpu);