From a5682a6335b7201bce75b66aa994314342bb4463 Mon Sep 17 00:00:00 2001
From: Gregory Nutt <gnutt@nuttx.org>
Date: Mon, 21 Jan 2019 07:37:33 -0600
Subject: [PATCH] Update TODO list
---
TODO | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)
diff --git a/TODO b/TODO
index cc39384ab4..5010c04eb6 100644
--- a/TODO
+++ b/TODO
@@ -1,4 +1,4 @@
-NuttX TODO List (Last updated January 7, 2019)
+NuttX TODO List (Last updated January 21, 2019)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This file summarizes known NuttX bugs, limitations, inconsistencies with
@@ -10,7 +10,7 @@ issues related to each board port.
nuttx/:
(16) Task/Scheduler (sched/)
- (4) SMP
+ (5) SMP
(1) Memory Management (mm/)
(0) Power Management (drivers/pm)
(3) Signals (sched/signal, arch/)
@@ -582,6 +582,38 @@ o SMP
an bugs caused by this. But I believe that failures are
possible.
+ Title: POSSIBLE FOR TWO CPUs TO HOLD A CRITICAL SECTION?
+ Description: The SMP design includes logic that will support multiple
+ CPUs holding a critical section. Is this necessary? How
+ can that occur? I think it can occur in the following
+ situation:
+
+ CPU0 - Task A is running.
+ - The CPU0 IDLE task is the only other task in the
+ CPU0 ready-to-run list.
+ CPU1 - Task B is running.
+ - Task C is blocked but remains in the ready-to-run
+ list because of a CPU affinity selection. Task C
+ also holds the critical section which is temporarily
+ relinquished because Task C is blocked by Task B.
+ - The CPU1 IDLE task is at the end of the list.
+
+ Actions:
+ 1. Task A/CPU 0 takes the critical section.
+ 2. Task B/CPU 1 suspends waiting for an event
+ 3. Task C is restarted.
+
+ Now both Task A and Task C hold the critical section.
+
+ This problem has never been observed, but seems to be a
+ possibility. I believe it could only occur if CPU affinity
+ is used (otherwise, tasks will pend must as when pre-
+ emption is disabled).
+Status: Open
+Priority: Unknown. Might be high, but first we would need to confirm
+ that this situation can occur and that is actually causes
+ a failure.
+
o Memory Management (mm/)
^^^^^^^^^^^^^^^^^^^^^^^