Commit 1362089d authored by Nikolay Borisov's avatar Nikolay Borisov Committed by David Sterba
Browse files

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: default avatarSu Yue <Damenly_Su@gmx.com>
Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarNikolay Borisov <nborisov@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 05840710

fs/btrfs/volumes.c

+38 −4
Original line number Diff line number Diff line
@@ -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

 *
@@ -765,6 +791,8 @@ 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_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);



			if (has_metadata_uuid)

				memcpy(fs_devices->metadata_uuid,

				       disk_super->metadata_uuid,

				       BTRFS_FSID_SIZE);

			else

				memcpy(fs_devices->metadata_uuid,

					disk_super->metadata_uuid, BTRFS_FSID_SIZE);

				       disk_super->fsid, BTRFS_FSID_SIZE);



			fs_devices->fsid_change = false;

		}

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