[PATCH 4.19 188/267] btrfs: include non-missing as a qualifier for the latest_bdev

Greg Kroah-Hartman
2020-06-19T16:17:29Z

From: Anand Jain <anand.jain@oracle.com>

commit 998a0671961f66e9fad4990ed75f80ba3088c2f1 upstream.

btrfs_free_extra_devids() updates fs_devices::latest_bdev to point to
the bdev with greatest device::generation number. For a typical-missing
device the generation number is zero so fs_devices::latest_bdev will
never point to it.

But if the missing device is due to alienation [1], then
device::generation is not zero and if it is greater or equal to the rest
of device generations in the list, then fs_devices::latest_bdev ends up
pointing to the missing device and reports the error like [2].

[1] We maintain devices of a fsid (as in fs_device::fsid) in the
fs_devices::devices list, a device is considered as an alien device
if its fsid does not match with the fs_device::fsid

Consider a working filesystem with raid1:

$ mkfs.btrfs -f -d raid1 -m raid1 /dev/sda /dev/sdb
$ mount /dev/sda /mnt-raid1
$ umount /mnt-raid1

While mnt-raid1 was unmounted the user force-adds one of its devices to
another btrfs filesystem:

$ mkfs.btrfs -f /dev/sdc
$ mount /dev/sdc /mnt-single
$ btrfs dev add -f /dev/sda /mnt-single

Now the original mnt-raid1 fails to mount in degraded mode, because
fs_devices::latest_bdev is pointing to the alien device.

$ mount -o degraded /dev/sdb /mnt-raid1

[2]
mount: wrong fs type, bad option, bad superblock on /dev/sdb,
missing codepage or helper program, or other error

In some cases useful info is found in syslog - try
dmesg | tail or so.

kernel: BTRFS warning (device sdb): devid 1 uuid 072a0192-675b-4d5a-8640-a5cf2b2c704d is missing
kernel: BTRFS error (device sdb): failed to read devices
kernel: BTRFS error (device sdb): open_ctree failed

Fix the root cause by checking if the device is not missing before it
can be considered for the fs_devices::latest_bdev.

CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/volumes.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -951,6 +951,8 @@ again:
&device->dev_state)) {
if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
&device->dev_state) &&
+ !test_bit(BTRFS_DEV_STATE_MISSING,
+ &device->dev_state) &&
(!latest_dev ||
device->generation > latest_dev->generation)) {
latest_dev = device;