// from subsys/usb/device/usb_device.c

int usb_write(uint8_t ep, const uint8_t *data, uint32_t data_len, uint32_t *bytes_ret)
{
    int tries = CONFIG_USB_NUMOF_EP_WRITE_RETRIES;
    int ret;

    do {
        ret = usb_dc_ep_write(ep, data, data_len, bytes_ret);
        if (ret == -EAGAIN) {
            LOG_WRN("Failed to write endpoint buffer 0x%02x", ep);
            k_yield();
        }

    } while (ret == -EAGAIN && tries--);

    return ret;
}

+bt
#0  z_priq_dumb_yield (pq=<optimized out>) at zephyr/kernel/include/priority_q.h:146
#1  runq_yield () at zephyr/kernel/sched.c:93
#2  z_impl_k_yield () at zephyr/kernel/sched.c:1056
#3  0x08002ec0 in k_yield ()
    at zephyr/stm32h753_mass_storage_ramdisk/zephyr/include/generated/zephyr/syscalls/kernel.h:184
#4  usb_write (ep=<optimized out>, data=data@entry=0x2400261f <csw> "USBS\001\001\001\001\020", data_len=data_len@entry=13, bytes_ret=bytes_ret@entry=0x0)
    at zephyr/subsys/usb/device/usb_device.c:1396
#5  0x08003d22 in sendCSW () at zephyr/subsys/usb/device/class/msc.c:288
#6  0x080048f4 in mass_storage_bulk_out (ep=<optimized out>, ep_status=<optimized out>)
    at zephyr/subsys/usb/device/class/msc.c:804
#7  0x080098e8 in HAL_PCD_DataOutStageCallback (hpcd=<optimized out>, epnum=<optimized out>)
    at zephyr/drivers/usb/device/usb_dc_stm32.c:1263
#8  0x0800ba8e in PCD_EP_OutXfrComplete_int (epnum=1, hpcd=0x24001a7c <usb_dc_stm32_state>)
    at modules/hal/stm32/stm32cube/stm32h7xx/drivers/src/stm32h7xx_hal_pcd.c:2291
#9  HAL_PCD_IRQHandler (hpcd=0x24001a7c <usb_dc_stm32_state>) at modules/hal/stm32/stm32cube/stm32h7xx/drivers/src/stm32h7xx_hal_pcd.c:1128
#10 0x08007c1a in _isr_wrapper () at zephyr/arch/arm/core/cortex_m/isr_wrapper.c:77
#11 <signal handler called>
#12 __ISB () at modules/hal/cmsis/CMSIS/Core/Include/cmsis_gcc.h:260
#13 arch_irq_unlock (key=0) at zephyr/include/zephyr/arch/arm/asm_inline_gcc.h:90
#14 arch_swap (key=0) at zephyr/arch/arm/include/cortex_m/kernel_arch_func.h:92
#15 z_swap_irqlock (key=0) at zephyr/kernel/include/kswap.h:207
#16 0x0800d134 in z_swap (key=..., lock=0x2404d671 <slice_expired>) at zephyr/kernel/include/kswap.h:218
#17 0x0800c99a in z_impl_k_sem_take (sem=sem@entry=0x2400198c <shell_uart_mpsc_buffer+40>, timeout=...) at zephyr/kernel/sem.c:158
#18 0x0800e85a in k_sem_take (timeout=..., sem=0x2400198c <shell_uart_mpsc_buffer+40>) at zephyr/stm32h753_mass_storage_ramdisk/zephyr/include/generated/zephyr/syscalls/kernel.h:1102
#19 mpsc_pbuf_alloc (buffer=buffer@entry=0x24001964 <shell_uart_mpsc_buffer>, wlen=wlen@entry=12, timeout=...) at zephyr/lib/os/mpsc_pbuf.c:385
#20 0x0800fc70 in copy_to_pbuffer (timeout=<optimized out>, msg=0x240006c0 <buf32+792>, mpsc_buffer=0x24001964 <shell_uart_mpsc_buffer>) at zephyr/subsys/shell/shell_log_backend.c:133
#21 process (backend=0x8013c7c <shell_uart_backend>, msg=0x240006c0 <buf32+792>) at zephyr/subsys/shell/shell_log_backend.c:242
#22 0x08001910 in log_backend_msg_process (msg=0x240006c0 <buf32+792>, backend=0x8013c7c <shell_uart_backend>) at zephyr/include/zephyr/logging/log_backend.h:182
#23 msg_process (msg=<optimized out>) at zephyr/subsys/logging/log_core.c:510
#24 z_impl_log_process () at zephyr/subsys/logging/log_core.c:566
#25 z_impl_log_process () at zephyr/subsys/logging/log_core.c:550
#26 0x08001a1c in log_process () at zephyr/stm32h753_mass_storage_ramdisk/zephyr/include/generated/zephyr/syscalls/log_ctrl.h:57
#27 log_process_thread_func (dummy1=<optimized out>, dummy2=<optimized out>, dummy3=<optimized out>) at zephyr/subsys/logging/log_core.c:965
#28 0x08001522 in z_thread_entry (entry=0x80019c9 <log_process_thread_func>, p1=0x0, p2=0x0, p3=0x0) at zephyr/lib/os/thread_entry.c:48
#29 0xaaaaaaaa in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

// from zephyr/kernel/sched.c

void z_impl_k_yield(void)
{
    __ASSERT(!arch_is_in_isr(), "");

    SYS_PORT_TRACING_FUNC(k_thread, yield);

    k_spinlock_key_t key = k_spin_lock(&_sched_spinlock);

    runq_yield();

    update_cache(1);
    z_swap(&_sched_spinlock, key);
}