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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 <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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1 changed files with 53 additions and 11 deletions
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@ -405,6 +405,21 @@ static noinline struct btrfs_fs_devices *find_fsid(
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return fs_devices;
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return fs_devices;
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}
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}
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}
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}
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/*
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* Handle scanned device having completed its fsid change but
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* belonging to a fs_devices that was created by a device that
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* has an outdated pair of fsid/metadata_uuid and
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* CHANGING_FSID_V2 flag set.
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*/
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list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
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if (fs_devices->fsid_change &&
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memcmp(fs_devices->metadata_uuid,
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fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
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memcmp(metadata_fsid, fs_devices->metadata_uuid,
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BTRFS_FSID_SIZE) == 0) {
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return fs_devices;
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}
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}
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}
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}
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/* Handle non-split brain cases */
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/* Handle non-split brain cases */
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@ -814,6 +829,30 @@ static struct btrfs_fs_devices *find_fsid_inprogress(
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return NULL;
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return NULL;
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}
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}
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static struct btrfs_fs_devices *find_fsid_changed(
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struct btrfs_super_block *disk_super)
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{
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struct btrfs_fs_devices *fs_devices;
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/*
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* Handles the case where scanned device is part of an fs that had
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* multiple successful changes of FSID but curently device didn't
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* observe it. Meaning our fsid will be different than theirs.
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*/
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list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
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if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
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BTRFS_FSID_SIZE) != 0 &&
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memcmp(fs_devices->metadata_uuid, disk_super->metadata_uuid,
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BTRFS_FSID_SIZE) == 0 &&
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memcmp(fs_devices->fsid, disk_super->fsid,
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BTRFS_FSID_SIZE) != 0) {
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return fs_devices;
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}
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}
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return NULL;
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}
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/*
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/*
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* Add new device to list of registered devices
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* Add new device to list of registered devices
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*
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*
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@ -835,17 +874,20 @@ static noinline struct btrfs_device *device_list_add(const char *path,
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bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
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bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
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BTRFS_SUPER_FLAG_CHANGING_FSID_V2);
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BTRFS_SUPER_FLAG_CHANGING_FSID_V2);
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if (fsid_change_in_progress && !has_metadata_uuid) {
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if (fsid_change_in_progress) {
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/*
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if (!has_metadata_uuid) {
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* When we have an image which has CHANGING_FSID_V2 set it might
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/*
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* belong to either a filesystem which has disks with completed
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* When we have an image which has CHANGING_FSID_V2 set
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* fsid change or it might belong to fs with no UUID changes in
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* it might belong to either a filesystem which has
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* effect, handle both.
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* disks with completed fsid change or it might belong
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*/
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* to fs with no UUID changes in effect, handle both.
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fs_devices = find_fsid_inprogress(disk_super);
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*/
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if (!fs_devices)
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fs_devices = find_fsid_inprogress(disk_super);
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fs_devices = find_fsid(disk_super->fsid, NULL);
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if (!fs_devices)
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fs_devices = find_fsid(disk_super->fsid, NULL);
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} else {
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fs_devices = find_fsid_changed(disk_super);
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}
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} else if (has_metadata_uuid) {
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} else if (has_metadata_uuid) {
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fs_devices = find_fsid(disk_super->fsid,
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fs_devices = find_fsid(disk_super->fsid,
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disk_super->metadata_uuid);
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disk_super->metadata_uuid);
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