btrfs: include non-missing as a qualifier for the latest_bdev
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>
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