Btrfs-progs: fix closing of devices

If a device could not be opened in volumes.c:read_one_dev(), a
btrfs_device instance was allocated and added to the list of
devices of the fs - however this device instance had its fd,
name and label fields not initialized. This is problematic in
disk-io.c:close_all_devices() as it tried to sync, fadvise and
close the (invalid) fd of the device, and kfree() its name and
label, which pointed to random memory locations.

  Thread 1 (Thread 0x7f0a3d2d1740 (LWP 23585)):
  #0  __GI___libc_free (mem=0xa5a5a5a5a5a5a5a5) at malloc.c:2970
  #1  0x000000000042054b in close_all_devices (fs_info=0x1e92bf0) at disk-io.c:1276
  #2  0x0000000000421dcd in close_ctree (root=<optimized out>) at disk-io.c:1336
  #3  0x0000000000418cfa in cmd_check (argc=<optimized out>, argv=<optimized out>) at cmds-check.c:4171
  #4  0x0000000000403ed4 in main (argc=2, argv=0x7fff9a583d28) at btrfs.c:295

v2: Added Liu Bo's review mention.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

Author: fdmanana

volumes.c

@@ -1631,10 +1631,10 @@ static int read_one_dev(struct btrfs_root *root,
 	if (!device) {
 		printk("warning devid %llu not found already\n",
 			(unsigned long long)devid);
-		device = kmalloc(sizeof(*device), GFP_NOFS);
+		device = kzalloc(sizeof(*device), GFP_NOFS);
 		if (!device)
 			return -ENOMEM;
-		device->total_ios = 0;
+		device->fd = -1;
 		list_add(&device->dev_list,
 			 &root->fs_info->fs_devices->devices);
 	}