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btrfs: Handle final split-brain possibility during fsid change

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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>
This commit is contained in:
Nikolay Borisov 2018-10-30 16:43:28 +02:00 committed by David Sterba
parent 7a62d0f073
commit cc5de4e702
1 changed files with 53 additions and 11 deletions
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64
fs/btrfs/volumes.c
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@ -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);