rp2: Fix recursive atomic sections when core1 is active.

mp_thread_begin_atomic_section() is expected to be recursive (i.e. for
nested machine.disable_irq() calls, or if Python code calls disable_irq()
and then the Python runtime calls mp_handle_pending() which also enters an
atomic section to check the scheduler state).

On rp2 when not using core1 the atomic sections are recursive.

However when core1 was active (i.e. _thread) then there was a bug that
caused the core to live-lock if an atomic section recursed.

Adds a test case specifically for mutual exclusion and recursive atomic
sections when using two threads. Without this fix the test immediately
hangs on rp2.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

2 files changed, 53 insertions, 0 deletions

diff --git a/tests/thread/disable_irq.py b/tests/thread/disable_irq.py
new file mode 100644
index 0000000000..3f1ac74f30
--- /dev/null
+++ b/tests/thread/disable_irq.py
@@ -0,0 +1,51 @@
+# Ensure that disabling IRQs creates mutual exclusion between threads
+# (also tests nesting of disable_irq across threads)
+import machine
+import time
+import _thread
+
+if not hasattr(machine, "disable_irq"):
+    print("SKIP")
+    raise SystemExit
+
+count = 0
+thread_done = False
+
+
+def inc_count():
+    global count
+    a = machine.disable_irq()
+    try:
+        count += 1
+        i = 0
+        while i < 20:
+            b = machine.disable_irq()
+            try:
+                count += 1
+                count -= 1
+                i += 1
+            finally:
+                machine.enable_irq(b)
+    finally:
+        machine.enable_irq(a)
+
+
+def inc_count_multiple(times):
+    for _ in range(times):
+        inc_count()
+
+
+def thread_entry(inc_times):
+    global thread_done
+    inc_count_multiple(inc_times)
+    thread_done = True
+
+
+_thread.start_new_thread(thread_entry, (1000,))
+inc_count_multiple(1000)
+
+time.sleep(1)
+
+print("count", count, thread_done)
+if count == 2000:
+    print("PASS")
diff --git a/tests/thread/disable_irq.py.exp b/tests/thread/disable_irq.py.exp
new file mode 100644
index 0000000000..2174b91d0d
--- /dev/null
+++ b/tests/thread/disable_irq.py.exp
@@ -0,0 +1,2 @@
+count 2000 True
+PASS