From: Nikolay Borisov Date: Tue, 30 Oct 2018 14:43:28 +0000 (+0200) Subject: btrfs: Handle final split-brain possibility during fsid change X-Git-Tag: 4.21-smb3-small-fixes~79^2~58 X-Git-Url: http://git.samba.org/samba.git/?p=sfrench%2Fcifs-2.6.git;a=commitdiff_plain;h=cc5de4e70256cbf4f28c0340e2d9f14cb6ed10aa btrfs: Handle final split-brain possibility during fsid change This patch lands the last case which needs to be handled by the fsid change code. Namely, this is the case where a multidisk filesystem has already undergone at least one successful fsid change i.e all disks have the METADATA_UUID incompat bit and power failure occurs as another fsid change is in progress. When such an event occurs, disks could be split in 2 groups. One of the groups will have both METADATA_UUID and CHANGING_FSID_V2 flags set coupled with old fsid/metadata_uuid pairs. The other group of disks will have only METADATA_UUID bit set and their fsid will be different than the one in disks in the first group. Here we look at the following cases: a) A disk from the first group is scanned first, so fs_devices is created with stale fsid/metdata_uuid. Then when a disk from the second group is scanned it needs to first check whether there exists such an fs_devices that has fsid_change set to true (because it was created with a disk having the CHANGING_FSID_V2 flag), the metadata_uuid and fsid of the fs_devices will be different (since it was created by a disk which already has had at least 1 successful fsid change) and finally the metadata_uuid of the fs_devices will equal that of the currently scanned disk (because metadata_uuid never really changes). When the correct fs_devices is found the information from the scanned disk will replace the current one in fs_devices since the scanned disk will have higher generation number. b) A disk from the second group is scanned so fs_devices is created as usual with differing fsid/metdata_uid. Then when a disk from the first group is scanned the code detects that it has both CHANGING_FSID_V2 and METADATA_UUID flags set and will search for fs_devices that has differing metadata_uuid/fsid and whose metadata_uuid is the same as that of the scanned device. Signed-off-by: Nikolay Borisov Signed-off-by: David Sterba --- diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index ce14ce068a84..a89596c3de56 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -405,6 +405,21 @@ static noinline struct btrfs_fs_devices *find_fsid( return fs_devices; } } + /* + * Handle scanned device having completed its fsid change but + * belonging to a fs_devices that was created by a device that + * has an outdated pair of fsid/metadata_uuid and + * CHANGING_FSID_V2 flag set. + */ + list_for_each_entry(fs_devices, &fs_uuids, fs_list) { + if (fs_devices->fsid_change && + memcmp(fs_devices->metadata_uuid, + fs_devices->fsid, BTRFS_FSID_SIZE) != 0 && + memcmp(metadata_fsid, fs_devices->metadata_uuid, + BTRFS_FSID_SIZE) == 0) { + return fs_devices; + } + } } /* Handle non-split brain cases */ @@ -814,6 +829,30 @@ static struct btrfs_fs_devices *find_fsid_inprogress( return NULL; } + +static struct btrfs_fs_devices *find_fsid_changed( + struct btrfs_super_block *disk_super) +{ + struct btrfs_fs_devices *fs_devices; + + /* + * Handles the case where scanned device is part of an fs that had + * multiple successful changes of FSID but curently device didn't + * observe it. Meaning our fsid will be different than theirs. + */ + list_for_each_entry(fs_devices, &fs_uuids, fs_list) { + if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid, + BTRFS_FSID_SIZE) != 0 && + memcmp(fs_devices->metadata_uuid, disk_super->metadata_uuid, + BTRFS_FSID_SIZE) == 0 && + memcmp(fs_devices->fsid, disk_super->fsid, + BTRFS_FSID_SIZE) != 0) { + return fs_devices; + } + } + + return NULL; +} /* * Add new device to list of registered devices * @@ -835,17 +874,20 @@ static noinline struct btrfs_device *device_list_add(const char *path, bool fsid_change_in_progress = (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_CHANGING_FSID_V2); - if (fsid_change_in_progress && !has_metadata_uuid) { - /* - * When we have an image which has CHANGING_FSID_V2 set it might - * belong to either a filesystem which has disks with completed - * fsid change or it might belong to fs with no UUID changes in - * effect, handle both. - */ - fs_devices = find_fsid_inprogress(disk_super); - if (!fs_devices) - fs_devices = find_fsid(disk_super->fsid, NULL); - + if (fsid_change_in_progress) { + if (!has_metadata_uuid) { + /* + * When we have an image which has CHANGING_FSID_V2 set + * it might belong to either a filesystem which has + * disks with completed fsid change or it might belong + * to fs with no UUID changes in effect, handle both. + */ + fs_devices = find_fsid_inprogress(disk_super); + if (!fs_devices) + fs_devices = find_fsid(disk_super->fsid, NULL); + } else { + fs_devices = find_fsid_changed(disk_super); + } } else if (has_metadata_uuid) { fs_devices = find_fsid(disk_super->fsid, disk_super->metadata_uuid);