[MIPS] RTLX: Protect rtlx_{read,write} with mutex.

Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/kernel/rtlx.c

···
 	wait_queue_head_t rt_queue;
 	wait_queue_head_t lx_queue;
 	atomic_t in_open;
+	struct mutex mutex;
 } channel_wqs[RTLX_CHANNELS];
 
 static struct irqaction irq;
···
 
 	lx = &rtlx->channel[index];
 
+	mutex_lock(&channel_wqs[index].mutex);
 	smp_rmb();
 	lx_write = lx->lx_write;
 
···
 	smp_wmb();
 	lx->lx_read = (lx->lx_read + count) % lx->buffer_size;
 	smp_wmb();
+	mutex_unlock(&channel_wqs[index].mutex);
 
 	return count;
 }
···
 
 	rt = &rtlx->channel[index];
 
+	mutex_lock(&channel_wqs[index].mutex);
 	smp_rmb();
 	rt_read = rt->rt_read;
 
···
 	smp_wmb();
 	rt->rt_write = (rt->rt_write + count) % rt->buffer_size;
 	smp_wmb();
+	mutex_unlock(&channel_wqs[index].mutex);
 
 	return count;
 }
···
 		init_waitqueue_head(&channel_wqs[i].rt_queue);
 		init_waitqueue_head(&channel_wqs[i].lx_queue);
 		atomic_set(&channel_wqs[i].in_open, 0);
+		mutex_init(&channel_wqs[i].mutex);
 
 		dev = device_create(mt_class, NULL, MKDEV(major, i),
 		                    "%s%d", module_name, i);