From 1362089d2ad7e20d16371b39d3c11990d4ec23e4 Mon Sep 17 00:00:00 2001 From: Nikolay Borisov Date: Fri, 10 Jan 2020 14:11:35 +0200 Subject: [PATCH] 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 Reviewed-by: Josef Bacik Signed-off-by: Nikolay Borisov Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 42 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 38 insertions(+), 4 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 7a30dd8ffdb5..9cfc668f91f4 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -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; }