Zephyr-RTOS logging with DMA on STM32L432KC - stm32

Question

I'm trying to run Zephyr Logging by using DMA on UART on STM32L432KC.
That's simple main loop:
#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(example, LOG_LEVEL_DBG);
int main(void)
{
while (1) {
LOG_INF("main loop");
k_msleep(1000);
}
}
That's full configuration:
CONFIG_SOC_SERIES_STM32L4X=y
CONFIG_SOC_STM32L432XX=y
# Enable MPU
CONFIG_ARM_MPU=y
# Enable HW stack protection
CONFIG_HW_STACK_PROTECTION=y
# enable uart driver
CONFIG_SERIAL=y
# enable GPIO
CONFIG_GPIO=y
# Enable Clocks
CONFIG_CLOCK_CONTROL=y
# console
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y
CONFIG_UART_ASYNC_API=y
# enable DMA
CONFIG_DMA=y
# enable pin controller
CONFIG_PINCTRL=y
# config logging
CONFIG_LOG=y
CONFIG_LOG_BACKEND_UART_ASYNC=y
CONFIG_LOG_MODE_IMMEDIATE=y
Then build it and flash:
west flash -b nucleo_l432kc
In logs I see following output:
*** Booting Zephyr OS build zephyr-v3.2.0-863-g78809549ee4c ***
[00:00:01.001,000] <inf> example: main loop
When I change CONFIG_LOG_MODE_IMMEDIATE=y to CONFIG_LOG_MODE_DEFERRED=y it prints log every second like I expect.
I discovered that code stops here on k_sem_take(&sem, K_FOREVER) and this uart_callback is never called to release this mutex.
Also discovered when following options are enabled it's working fine with CONFIG_LOG_MODE_DEFERRED=y option:
CONFIG_LOG_PROCESS_THREAD=y
CONFIG_LOG_PROCESS_THREAD_SLEEP_MS=100
But that makes me wondering why another thread must be created? DMA is no blocking. Really confusing.
What am I missing? I would like to delegate all logging to DMA buffer with Logging subsystem features, without additional threads and buffering. Is there someone experienced who can point what is wrong?