From 9aedf1bdec85ff067999e89b8d1638cc3703c652 Mon Sep 17 00:00:00 2001
From: Gregory Nutt <gnutt@nuttx.org>
Date: Sun, 25 Dec 2016 06:54:43 -0600
Subject: [PATCH] SMP:  Fix a error introduced in
 36b676eea6f132916f806587a8dffe7b3040473d and fully decouple disabling of
 pre-emption from critical sections.

---
 sched/irq/irq_csection.c   | 30 ------------------------------
 sched/sched/sched_unlock.c | 10 +++++-----
 2 files changed, 5 insertions(+), 35 deletions(-)

diff --git a/sched/irq/irq_csection.c b/sched/irq/irq_csection.c
index c9f9f91c18..5b517de8bb 100644
--- a/sched/irq/irq_csection.c
+++ b/sched/irq/irq_csection.c
@@ -507,36 +507,6 @@ 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();
-                    }
-                }
             }
         }
     }
diff --git a/sched/sched/sched_unlock.c b/sched/sched/sched_unlock.c
index ff676c827a..df783dee7b 100644
--- a/sched/sched/sched_unlock.c
+++ b/sched/sched/sched_unlock.c
@@ -102,7 +102,8 @@ int sched_unlock(void)
 
 #ifdef CONFIG_SMP
           /* The lockcount has decremented to zero and we need to perform
-           * release our hold on the lock.
+           * release our hold on the lock.  Pre-emption may still be locked
+           * from other CPUs.
            */
 
           DEBUGASSERT(g_cpu_schedlock == SP_LOCKED &&
@@ -118,13 +119,12 @@ 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();
             }