From fbc6feaec98ac0c6a615bbe9e17c5689a1a84650 Mon Sep 17 00:00:00 2001 From: Nikolay Borisov Date: Tue, 30 Oct 2018 16:43:25 +0200 Subject: [PATCH] btrfs: Add handling for disk split-brain scenario during fsid change Even though fsid change without rewrite is a very quick operation it's still possible to experience a split-brain scenario if power loss occurs at the most inconvenient time. This patch handles the case where power failure occurs while the first transaction (the one setting CHANGING_FSID_V2) flag is being persisted on disk. This can cause the btrfs_fs_devices of this filesystem to be created by a device which: a) has the CHANGING_FSID_V2 flag set but its fsid value is intact b) or a device which doesn't have CHANGING_FSID_V2 flag set and its fsid value is intact This situation is trivially handled by the current find_fsid code since in both cases the devices are going to be treated like ordinary devices. Since btrfs is always mounted using the superblock of the latest device (the one with highest generation number), meaning it will have the CHANGING_FSID_V2 flag set, ensure it's being cleared on mount. On the first transaction commit following mount all disks will have it cleared. Signed-off-by: Nikolay Borisov Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/disk-io.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index ed6d4c83c1e7..feb67dfd663d 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -2799,10 +2799,10 @@ int open_ctree(struct super_block *sb, * the whole block of INFO_SIZE */ memcpy(fs_info->super_copy, bh->b_data, sizeof(*fs_info->super_copy)); - memcpy(fs_info->super_for_commit, fs_info->super_copy, - sizeof(*fs_info->super_for_commit)); brelse(bh); + disk_super = fs_info->super_copy; + ASSERT(!memcmp(fs_info->fs_devices->fsid, fs_info->super_copy->fsid, BTRFS_FSID_SIZE)); @@ -2812,6 +2812,16 @@ int open_ctree(struct super_block *sb, BTRFS_FSID_SIZE)); } + features = btrfs_super_flags(disk_super); + if (features & BTRFS_SUPER_FLAG_CHANGING_FSID_V2) { + features &= ~BTRFS_SUPER_FLAG_CHANGING_FSID_V2; + btrfs_set_super_flags(disk_super, features); + btrfs_info(fs_info, + "found metadata UUID change in progress flag, clearing"); + } + + memcpy(fs_info->super_for_commit, fs_info->super_copy, + sizeof(*fs_info->super_for_commit)); ret = btrfs_validate_mount_super(fs_info); if (ret) { @@ -2820,7 +2830,6 @@ int open_ctree(struct super_block *sb, goto fail_alloc; } - disk_super = fs_info->super_copy; if (!btrfs_super_root(disk_super)) goto fail_alloc; -- 2.30.2