This patch prevent heap corruption as in below case.

TASK A                        TASK B
                              malloc()
                              mm_takesemaphore()
                              heap holder is set to TASK B
                         <--- preempt
...
task_exit()
Set to current task to
  TASK B
Try to release tcb, and
  stack memory
free()
mm_takesemaphore()
  - Successfully obtain
    semaphore because current
    task and heap holder is
    same.
Free memory....
Heap corrupt.

This change forces all de-allocations via sched_kfree() and sched_ufree()
to be delayed.  Eliminating the immediate de-allocation prevents the
above problem with the the re-entrant semaphore because the deallocation
always occurs on the worker thread, never on TASK B.

There could be consequences in the timing of memory availability.  We
will see.

sched/sched/sched_free.c

@@ -85,8 +85,6 @@ void sched_ufree(FAR void *address)
    * must have exclusive access to the memory manager to do this.
    */
 
-  if (up_interrupt_context() || kumm_trysemaphore() != 0)
-    {
   irqstate_t flags;
 
   /* Yes.. Make sure that this is not a attempt to free kernel memory
@@ -108,14 +106,6 @@ void sched_ufree(FAR void *address)
 
   sched_signal_free();
   leave_critical_section(flags);
-    }
-  else
-    {
-      /* No.. just deallocate the memory now. */
-
-      kumm_free(address);
-      kumm_givesemaphore();
-    }
 #endif
 }
 
@@ -129,8 +119,6 @@ void sched_kfree(FAR void *address)
    * must have exclusive access to the memory manager to do this.
    */
 
-  if (up_interrupt_context() || kmm_trysemaphore() != 0)
-    {
     /* Yes.. Make sure that this is not a attempt to free user memory
      * using the kernel deallocator.
      */
@@ -148,14 +136,6 @@ void sched_kfree(FAR void *address)
     sched_signal_free();
     leave_critical_section(flags);
 }
-  else
-    {
-      /* No.. just deallocate the memory now. */
-
-      kmm_free(address);
-      kmm_givesemaphore();
-    }
-}
 #endif
 
 /****************************************************************************