Revert "SMP: Fix a error introduced in 36b676eea6 and fully decouple disabling of pre-emption from critical sections."

This reverts commit 9aedf1bdec.

sched/irq/irq_csection.c

@@ -507,6 +507,36 @@ void leave_critical_section(irqstate_t flags)
               rtcb->irqcount = 0;
               spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
                           &g_cpu_irqlock);
+
+              /* Have all CPUs released the lock? */
+
+              if (!spin_islocked(&g_cpu_irqlock))
+                {
+                  /* Check if there are pending tasks and that pre-emption
+                   * is also enabled.
+                   *
+                   * REVISIT: Is there an issue here?  up_release_pending()
+                   * must be called from within a critical section but here
+                   * we have just left the critical section.  At least we
+                   * still have interrupts disabled on this CPU.
+                   */
+
+                  if (g_pendingtasks.head != NULL &&
+                      !spin_islocked(&g_cpu_schedlock))
+                    {
+                      /* Release any ready-to-run tasks that have collected
+                       * in g_pendingtasks if the scheduler is not locked.
+                       *
+                       * NOTE: This operation has a very high likelihood of
+                       * causing this task to be switched out!
+                       *
+                       * REVISIT: Should this not be done while we are in the
+                       * critical section.
+                       */
+
+                      up_release_pending();
+                    }
+                }
             }
         }
     }

sched/sched/sched_unlock.c

@@ -102,8 +102,7 @@ int sched_unlock(void)
 
 #ifdef CONFIG_SMP
           /* The lockcount has decremented to zero and we need to perform
-           * release our hold on the lock.  Pre-emption may still be locked
+           * release our hold on the lock.
-           * from other CPUs.
            */
 
           DEBUGASSERT(g_cpu_schedlock == SP_LOCKED &&
@@ -119,12 +118,13 @@ int sched_unlock(void)
            *
            * NOTE: This operation has a very high likelihood of causing
            * this task to be switched out!
-           *
-           * NOTE: In SMP mode, pre-emption may still be locked due to
-           * operations on other CPUs.
            */
 
+#ifdef CONFIG_SMP
+          if (!spin_islocked(&g_cpu_schedlock) && g_pendingtasks.head != NULL)
+#else
           if (g_pendingtasks.head != NULL)
+#endif
             {
               up_release_pending();
             }