[PATCH v2] btrfs: free device without BTRFS_MAGIC

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

Many things can happen after the device is scanned and before the device
is mounted.

One such thing is losing the BTRFS_MAGIC on the device.

If it happens we still won't free that device from the memory and causes
the userland to confuse.

For example: As the BTRFS_IOC_DEV_INFO still carries the device path which
does not have the BTRFS_MAGIC, the btrfs fi show still shows device
which does not belong. As shown below.

mkfs.btrfs -fq -draid1 -mraid1 /dev/sda /dev/sdb

wipefs -a /dev/sdb
mount -o degraded /dev/sda /btrfs
btrfs fi show -m

/dev/sdb does not contain BTRFS_MAGIC and we still show it as part of
btrfs.
Label: none  uuid: 470ec6fb-646b-4464-b3cb-df1b26c527bd
        Total devices 2 FS bytes used 128.00KiB
        devid    1 size 3.00GiB used 571.19MiB path /dev/sda
        devid    2 size 3.00GiB used 571.19MiB path /dev/sdb

Fix is to return -ENODATA error code in btrfs_read_dev_one_super()
when BTRFS_MAGIC check fails, and its parent open_fs_devices() to
free the device in the mount-thread.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
v2: Do not return ENODATA on `btrfs_super_bytenr(super) != bytenr`

 fs/btrfs/disk-io.c |  8 ++++++--
 fs/btrfs/volumes.c | 19 +++++++++++++------
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 160b485d2cc0..d84a49fe9639 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3429,12 +3429,16 @@ struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
 		return ERR_CAST(page);
 
 	super = page_address(page);
-	if (btrfs_super_bytenr(super) != bytenr ||
-		    btrfs_super_magic(super) != BTRFS_MAGIC) {
+	if (btrfs_super_bytenr(super) != bytenr) {
 		btrfs_release_disk_super(super);
 		return ERR_PTR(-EINVAL);
 	}
 
+	if (btrfs_super_magic(super) != BTRFS_MAGIC) {
+		btrfs_release_disk_super(super);
+		return ERR_PTR(-ENODATA);
+	}
+
 	return super;
 }
 
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 7cc677a7e544..ec9dac40b4f1 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1198,17 +1198,24 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
 {
 	struct btrfs_device *device;
 	struct btrfs_device *latest_dev = NULL;
+	struct btrfs_device *tmp_device;
 
 	flags |= FMODE_EXCL;
 
-	list_for_each_entry(device, &fs_devices->devices, dev_list) {
-		/* Just open everything we can; ignore failures here */
-		if (btrfs_open_one_device(fs_devices, device, flags, holder))
-			continue;
+	list_for_each_entry_safe(device, tmp_device, &fs_devices->devices,
+				 dev_list) {
+		int ret;
 
-		if (!latest_dev ||
-		    device->generation > latest_dev->generation)
+		/* Just open everything we can; ignore failures here */
+		ret = btrfs_open_one_device(fs_devices, device, flags, holder);
+		if (ret == 0 && (!latest_dev ||
+		    device->generation > latest_dev->generation)) {
 			latest_dev = device;
+		} else if (ret == -ENODATA) {
+			fs_devices->num_devices--;
+			list_del(&device->dev_list);
+			btrfs_free_device(device);
+		}
 	}
 	if (fs_devices->open_devices == 0)
 		return -EINVAL;
-- 
2.25.1