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 @@ -1042,6 +1042,8 @@ 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;