[ALSA] mpu401: fix recursive locking in timer

When the output and input ports are used at the same time, the timer can
be interrupted by the hardware interrupt, so we have to disable
interrupts when we take a lock in the timer.
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
Signed-off-by: NJaroslav Kysela <perex@perex.cz>

sound/drivers/mpu401/mpu401_uart.c

@@ -97,23 +97,27 @@ static void snd_mpu401_uart_clear_rx(struct snd_mpu401 *mpu)
 
 static void uart_interrupt_tx(struct snd_mpu401 *mpu)
 {
+	unsigned long flags;
+
 	if (test_bit(MPU401_MODE_BIT_OUTPUT, &mpu->mode) &&
 	    test_bit(MPU401_MODE_BIT_OUTPUT_TRIGGER, &mpu->mode)) {
-		spin_lock(&mpu->output_lock);
+		spin_lock_irqsave(&mpu->output_lock, flags);
 		snd_mpu401_uart_output_write(mpu);
-		spin_unlock(&mpu->output_lock);
+		spin_unlock_irqrestore(&mpu->output_lock, flags);
 	}
 }
 
 static void _snd_mpu401_uart_interrupt(struct snd_mpu401 *mpu)
 {
+	unsigned long flags;
+
 	if (mpu->info_flags & MPU401_INFO_INPUT) {
-		spin_lock(&mpu->input_lock);
+		spin_lock_irqsave(&mpu->input_lock, flags);
 		if (test_bit(MPU401_MODE_BIT_INPUT, &mpu->mode))
 			snd_mpu401_uart_input_read(mpu);
 		else
 			snd_mpu401_uart_clear_rx(mpu);
-		spin_unlock(&mpu->input_lock);
+		spin_unlock_irqrestore(&mpu->input_lock, flags);
 	}
 	if (! (mpu->info_flags & MPU401_INFO_TX_IRQ))
 		/* ok. for better Tx performance try do some output