stdio hardening + new mutex API (#1224)

* * Harden stdio_usb and stdio in general against deadlocks which could otherwise result from doing printfs from within IRQs
* Add a test for the above
* Add mutex_try_enter_block_until API.
* Make best_effort_wfe_or_timeout not use alarms if called from within IRQ

test/pico_stdio_test/CMakeLists.txt

@@ -0,0 +1,16 @@
+if (NOT PICO_TIME_NO_ALARM_SUPPORT)
+    add_executable(pico_stdio_test_uart pico_stdio_test.c)
+    target_link_libraries(pico_stdio_test_uart PRIVATE pico_stdlib pico_test pico_multicore)
+    pico_add_extra_outputs(pico_stdio_test_uart)
+    pico_enable_stdio_uart(pico_stdio_test_uart 1)
+    pico_enable_stdio_usb(pico_stdio_test_uart 0)
+
+    add_executable(pico_stdio_test_usb pico_stdio_test.c)
+    target_link_libraries(pico_stdio_test_usb PRIVATE pico_stdlib pico_test pico_multicore)
+    target_compile_definitions(pico_stdio_test_usb PRIVATE
+            PICO_STDIO_USB_CONNECT_WAIT_TIMEOUT_MS=-1) # wait for USB connect
+
+    pico_add_extra_outputs(pico_stdio_test_usb)
+    pico_enable_stdio_uart(pico_stdio_test_usb 0)
+    pico_enable_stdio_usb(pico_stdio_test_usb 1)
+endif()

test/pico_stdio_test/pico_stdio_test.c

@@ -0,0 +1,57 @@
+/**
+ * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "pico/multicore.h"
+#include "pico/test.h"
+
+PICOTEST_MODULE_NAME("pico_stdio_test", "pico_stdio test harness");
+
+static volatile bool deadlock_test_done;
+static void deadlock_test_core1(void) {
+    busy_wait_ms(250);
+    for(int i=0;i<1000;i++) {
+        if (deadlock_test_done) break;
+        printf("Hello from core 1 - %d\n", i);
+        busy_wait_ms(23);
+    }
+}
+
+static volatile bool deadlock_test_irq_called;
+
+static int64_t deadlock_test_alarm(alarm_id_t id, void *param) {
+    static int foo;
+    printf("Here is a printf from the IRQ %d\n", ++foo);
+    deadlock_test_irq_called = true;
+    return 100;
+}
+
+int main() {
+    stdio_init_all();
+
+    for(int i=0;i<10;i++) {
+        printf("Hello %d\n", i);
+    }
+    printf("pico_stdio_test begins\n");
+    PICOTEST_START();
+
+    // Check default config has valid data in it
+    PICOTEST_START_SECTION("STDIO deadlock test");
+    multicore_launch_core1(deadlock_test_core1);
+    alarm_id_t alarm_id = add_alarm_in_ms(500, deadlock_test_alarm, NULL, false);
+    PICOTEST_CHECK(getchar_timeout_us(2000000) < 0, "someone pressed a key!");
+
+    deadlock_test_done = true;
+    cancel_alarm(alarm_id);
+
+    sleep_ms(100);
+    PICOTEST_CHECK(deadlock_test_irq_called, "deadlock_test_irq was not called");
+    PICOTEST_END_SECTION();
+
+    PICOTEST_END_TEST();
+}
+