[PATCH 5.5 331/399] btrfs: Fix split-brain handling when changing FSID to metadata uuid

Greg Kroah-Hartman
2020-02-21T08:41:04Z

From: Nikolay Borisov <nborisov@suse.com>

[ Upstream commit 1362089d2ad7e20d16371b39d3c11990d4ec23e4 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 c5c0dc0cbf517..a8b71ded4d212 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -723,6 +723,32 @@ 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
*
@@ -762,7 +788,9 @@ static noinline struct btrfs_device *device_list_add(const char *path,
fs_devices = find_fsid(disk_super->fsid,
disk_super->metadata_uuid);
} 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);
}

@@ -792,12 +820,18 @@ 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;
}
--
2.20.1