[PATCH 4/4] btrfs: free alien device due to device add

[Anand Jain <anand.jain@oracle.com>]

When the old device has new fsid through btrfs device add -f <dev> our
fs_devices list has an alien device in one of the fs_devices.

By having an alien device in fs_devices, we have two issues so far

1. missing device is not shows as missing in the userland

Which is due to cracks in the function btrfs_open_one_device() and
hardened by patch
 btrfs: delete identified alien device in open_fs_devices

2. mount of a degraded fs_devices fails

Which is due to cracks in the function btrfs_free_extra_devids() and
hardened by patch
 btrfs: include non-missing as a qualifier for the latest_bdev

Now the reason for both of this issue is that there is an alien (does not
contain the intended fsid) device in the fs_devices.

We know a device can be scanned/added through
btrfs-control::BTRFS_IOC_SCAN_DEV|BTRFS_IOC_DEVICES_READY
or by
ioctl::BTRFS_IOC_ADD_DEV

And device coming through btrfs-control is checked against the all other
devices in btrfs kernel but not coming through BTRFS_IOC_ADD_DEV.

This patch checks if the device add is alienating any other scanned
device and deletes it.

In fact, this patch fixes both the issues 1 and 2 (above) by eliminating
the source of the issue, but still they have their own patch as well
because its the right way to harden the functions and fill the cracks.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/volumes.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6c42048ec099..f8b21e82df2a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2736,6 +2736,19 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 
 	/* Update ctime/mtime for libblkid */
 	update_dev_time(device_path);
+
+	/*
+	 * Now that we have written a new sb into this device, check all other
+	 * fs_devices list if it alienates any scanned device.
+	 */
+	mutex_lock(&uuid_mutex);
+	/*
+	 * Ignore the return as we are successfull in the core task - to added
+	 * the device
+	 */
+	btrfs_free_stale_devices(device_path, NULL);
+	mutex_unlock(&uuid_mutex);
+
 	return ret;
 
 error_sysfs:
-- 
1.8.3.1