drivers: char: tlclk.c: Avoid data race between init and interrupt handler

After registering character device the file operation callbacks can be
called. The open callback registers interrupt handler.
Therefore interrupt handler can execute in parallel with rest of the init
function. To avoid such data race initialize telclk_interrupt variable
and struct alarm_events before registering character device.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Link: https://lore.kernel.org/r/20200417153451.1551-1-madhuparnabhowmik10@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/tlclk.c

@@ -777,18 +777,22 @@ static int __init tlclk_init(void)
 {
 	int ret;
 
-	ret = register_chrdev(tlclk_major, "telco_clock", &tlclk_fops);
-	if (ret < 0) {
-		printk(KERN_ERR "tlclk: can't get major %d.\n", tlclk_major);
-		return ret;
-	}
-	tlclk_major = ret;
+	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
+
 	alarm_events = kzalloc( sizeof(struct tlclk_alarms), GFP_KERNEL);
 	if (!alarm_events) {
 		ret = -ENOMEM;
 		goto out1;
 	}
 
+	ret = register_chrdev(tlclk_major, "telco_clock", &tlclk_fops);
+	if (ret < 0) {
+		printk(KERN_ERR "tlclk: can't get major %d.\n", tlclk_major);
+		kfree(alarm_events);
+		return ret;
+	}
+	tlclk_major = ret;
+
 	/* Read telecom clock IRQ number (Set by BIOS) */
 	if (!request_region(TLCLK_BASE, 8, "telco_clock")) {
 		printk(KERN_ERR "tlclk: request_region 0x%X failed.\n",
@@ -796,7 +800,6 @@ static int __init tlclk_init(void)
 		ret = -EBUSY;
 		goto out2;
 	}
-	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
 
 	if (0x0F == telclk_interrupt ) { /* not MCPBL0010 ? */
 		printk(KERN_ERR "telclk_interrupt = 0x%x non-mcpbl0010 hw.\n",
@@ -837,8 +840,8 @@ out3:
 	release_region(TLCLK_BASE, 8);
 out2:
 	kfree(alarm_events);
-out1:
 	unregister_chrdev(tlclk_major, "telco_clock");
+out1:
 	return ret;
 }