STM32F407 Uart Rx inturrupts misses some characters - uart

Question

UART sometimes lost some characters while communicate with all other devices.
I tried communication with arduino, serial monitor(At PC, with serial-usb converter), HM-10 Bluetooth module.
In every case, my stm32f407 misses some characters when receive data.
(I checked it with LCD. I don't send any data with uart.)
For example, when I send send "This is test string" from PC,
The incoming string is like "Ths is tt sring".
There are no bad characters. It only misses some characters.
In handler, I commented USART_Cmd(...), moved USART_ClearITPendingBit(USART3, USART_IT_RXNE); to the bottom, and changed priority to 0,1,2,3.
However, nothing changed.
My clock is 168MHz and uart uses 9600, or 115200 baudrate.
Both have same problem.
Below is my code.
For some reasons, I can't use HAL driver.
void Uart_Init(long uart_baudrate) {
GPIO_InitTypeDef GPIO_InitStructure;
USART_InitTypeDef USART_InitStructure;
/* GPIO Periph clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);
// USART1 Port Configuration (TX - 9, RX - 10)
GPIO_StructInit(&GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10 | GPIO_Pin_11;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_Init(GPIOB, &GPIO_InitStructure);
/* Connect USART pins to AF */
GPIO_PinAFConfig(GPIOB, GPIO_PinSource10, GPIO_AF_USART3);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource11, GPIO_AF_USART3);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
USART_StructInit(&USART_InitStructure);
USART_InitStructure.USART_BaudRate = uart_baudrate;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
USART_Init(USART3, &USART_InitStructure);
USART_Cmd(USART3, ENABLE);
}
#define UART_BUF_LEN 64
volatile static char uartBuffer[UART_BUF_LEN];
volatile static int uartBufferIn = 0;
volatile static int uartBufferOut = 0;
//Uart rx handler
void USART3_IRQHandler(void){
unsigned int st1;
st1 = __disable_interrupts();
if(USART_GetITStatus(USART3, USART_IT_RXNE) == SET){
USART_ClearITPendingBit(USART3, USART_IT_RXNE);
uartBuffer[uartBufferIn] = USART_ReceiveData(USART3);
uartBufferIn++;
if(uartBufferIn==uartBufferOut)uartBufferOut++;
uartBufferIn&=0x3F;
uartBufferOut&=0x3F;
}
USART_Cmd(USART3, ENABLE);
__restore_interrupts(st1);
}
//Enable uart rx interrupt
void Uart_Start(void){
unsigned int st1;
st1 = __disable_interrupts();
NVIC_InitTypeDef NVIC_InitStructure;
VectorTable->USART3_IRQHANDLER = USART3_IRQHandler;
NVIC_InitStructure.NVIC_IRQChannel = USART3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
USART_Cmd(USART3, ENABLE);
USART_ITConfig(USART3, USART_IT_RXNE, ENABLE);
__restore_interrupts(st1);
}