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btrfs: Fix split-brain handling when changing FSID to metadata uuid 

Current code doesn't correctly handle the situation which arises when
a file system that has METADATA_UUID_INCOMPAT flag set and has its FSID
changed to the one in metadata uuid. This causes the incompat flag to
disappear.

In case of a power failure we could end up in a situation where part of
the disks in a multi-disk filesystem are correctly reverted to
METADATA_UUID_INCOMPAT flag unset state, while others have
METADATA_UUID_INCOMPAT set and CHANGING_FSID_V2_IN_PROGRESS.

This patch corrects the behavior required to handle the case where a
disk of the second type is scanned first, creating the necessary
btrfs_fs_devices. Subsequently, when a disk which has already completed
the transition is scanned it should overwrite the data in
btrfs_fs_devices.

Reported-by: Su Yue <Damenly_Su@gmx.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov 2020-01-10 14:11:35 +02:00 committed by David Sterba
parent 0584071014
commit 1362089d2a
1 changed files with 38 additions and 4 deletions
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42
fs/btrfs/volumes.c
View File

@ -736,6 +736,32 @@ static struct btrfs_fs_devices *find_fsid_changed(
return NULL;
}
static struct btrfs_fs_devices *find_fsid_reverted_metadata(
struct btrfs_super_block *disk_super)
{
struct btrfs_fs_devices *fs_devices;
/*
* Handle the case where the scanned device is part of an fs whose last
* metadata UUID change reverted it to the original FSID. At the same
* time * fs_devices was first created by another constitutent device
* which didn't fully observe the operation. This results in an
* btrfs_fs_devices created with metadata/fsid different AND
* btrfs_fs_devices::fsid_change set AND the metadata_uuid of the
* fs_devices equal to the FSID of the disk.
*/
list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
if (memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
BTRFS_FSID_SIZE) != 0 &&
memcmp(fs_devices->metadata_uuid, disk_super->fsid,
BTRFS_FSID_SIZE) == 0 &&
fs_devices->fsid_change)
return fs_devices;
}
return NULL;
}
/*
* Add new device to list of registered devices
*
@ -765,7 +791,9 @@ static noinline struct btrfs_device *device_list_add(const char *path,
} else if (has_metadata_uuid) {
fs_devices = find_fsid_with_metadata_uuid(disk_super);
} else {
fs_devices = find_fsid(disk_super->fsid, NULL);
fs_devices = find_fsid_reverted_metadata(disk_super);
if (!fs_devices)
fs_devices = find_fsid(disk_super->fsid, NULL);
}
@ -795,12 +823,18 @@ static noinline struct btrfs_device *device_list_add(const char *path,
* a device which had the CHANGING_FSID_V2 flag then replace the
* metadata_uuid/fsid values of the fs_devices.
*/
if (has_metadata_uuid && fs_devices->fsid_change &&
if (fs_devices->fsid_change &&
found_transid > fs_devices->latest_generation) {
memcpy(fs_devices->fsid, disk_super->fsid,
BTRFS_FSID_SIZE);
memcpy(fs_devices->metadata_uuid,
disk_super->metadata_uuid, BTRFS_FSID_SIZE);
if (has_metadata_uuid)
memcpy(fs_devices->metadata_uuid,
disk_super->metadata_uuid,
BTRFS_FSID_SIZE);
else
memcpy(fs_devices->metadata_uuid,
disk_super->fsid, BTRFS_FSID_SIZE);
fs_devices->fsid_change = false;
}