Calling logging functions from a thread hangs Zephyr when using USB UART

[fcgdam]

So not sure if this is an issue, or bad use of my part, but anyway:

I'm testing some simple things and among them, instead of calling printk, is using the logging functions LOG_INF, LOG_WRN, and so on.

Basically when using a STM32 board (STM32F411RE), enabling USB and redirecting the LOG output to the USB UART, calling the log functions from the starting main thread, it works fine until a thread is created and from the created Thread the LOG_* functions are called. When this happens, Zephyr crashes.

My example:

prj.conf

CONFIG_ASSERT=y
CONFIG_LOG=y
CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=2048
CONFIG_LOG_PROCESS_THREAD=y     # It also fails with a specific thread for logging
CONFIG_LOG_BACKEND_UART=y
#CONFIG_LOG_MODE_DEFERRED=y
#CONFIG_LOG_MODE_MINIMAL=y   
CONFIG_PRINTK=y

CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y
CONFIG_UART_LINE_CTRL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_STDOUT_CONSOLE=y

# Activate the USB driver
CONFIG_USB_DEVICE_STACK=y
CONFIG_USB_DEVICE_PRODUCT="ZEPHYR"
CONFIG_USB_DEVICE_PID=0x0001
CONFIG_USB_DEVICE_VID=0x4010
CONFIG_USB_DRIVER_LOG_LEVEL_ERR=y
CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT=n

The overlay file to enable the console over USB:
usb.overlay

/ {
    chosen {
        zephyr,console= &cdc_acm_uart0;
    };
};

&zephyr_udc0 {
    cdc_acm_uart0: cdc_acm_uart0 {
        compatible = "zephyr,cdc-acm-uart";
        label = "CDC_ACM_0";
    };
};

And the code main.c:

#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/logging/log.h>
#include <zephyr/usb/usb_device.h>

LOG_MODULE_REGISTER(zthreadlog);

void    task_log( ) {

    k_msleep(5000);         // Avoids the hang right at the startup and allows to connect to USB

    while ( true ) {
        LOG_INF("Hello World from thread!");        // It hangs in here. Zephyr RTOS crashes.
        //printk("Hello World from thread!!");         // printk works just fine.
        k_msleep(2200);
    }
}

int    main( void ) {
int ret;

    ret = usb_enable(NULL);

    k_msleep( 1000 );

    LOG_INF("Started:");

    while ( true ) {
        LOG_INF("Hello World!");
        k_msleep(2000);
    }

    return 0;
}

K_THREAD_DEFINE( TASK_LOG_id, 256, task_log, NULL, NULL, NULL, 14, 0 , 0);

So any idea why this happens?

Zephyr kernel versions tested:

• 3.5.0
• 3.6.0_rc2 -> In this the issue is even worse, since a lot of garbage is writen on the terminal and USB driver crashes and disconnects.

[fcgdam]

For future reference: My problem. Stack was too small (256 bytes). Increasing the stack, solved the issue.