From: Qu Wenruo wqu@suse.com
commit 30d40577e322b670551ad7e2faa9570b6e23eb2b upstream.
[BUG] When a fs has orphan reloc tree along with unfinished balance: ... item 16 key (TREE_RELOC ROOT_ITEM FS_TREE) itemoff 12090 itemsize 439 generation 12 root_dirid 256 bytenr 300400640 level 1 refs 0 <<< lastsnap 8 byte_limit 0 bytes_used 1359872 flags 0x0(none) uuid 7c48d938-33a3-4aae-ab19-6e5c9d406e46 item 17 key (BALANCE TEMPORARY_ITEM 0) itemoff 11642 itemsize 448 temporary item objectid BALANCE offset 0 balance status flags 14
Then at mount time, we can hit the following kernel BUG_ON(): BTRFS info (device dm-3): relocating block group 298844160 flags metadata|dup ------------[ cut here ]------------ kernel BUG at fs/btrfs/relocation.c:1413! invalid opcode: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 897 Comm: btrfs-balance Tainted: G O 5.2.0-rc1-custom #15 RIP: 0010:create_reloc_root+0x1eb/0x200 [btrfs] Call Trace: btrfs_init_reloc_root+0x96/0xb0 [btrfs] record_root_in_trans+0xb2/0xe0 [btrfs] btrfs_record_root_in_trans+0x55/0x70 [btrfs] select_reloc_root+0x7e/0x230 [btrfs] do_relocation+0xc4/0x620 [btrfs] relocate_tree_blocks+0x592/0x6a0 [btrfs] relocate_block_group+0x47b/0x5d0 [btrfs] btrfs_relocate_block_group+0x183/0x2f0 [btrfs] btrfs_relocate_chunk+0x4e/0xe0 [btrfs] btrfs_balance+0x864/0xfa0 [btrfs] balance_kthread+0x3b/0x50 [btrfs] kthread+0x123/0x140 ret_from_fork+0x27/0x50
[CAUSE] In btrfs, reloc trees are used to record swapped tree blocks during balance. Reloc tree either get merged (replace old tree blocks of its parent subvolume) in next transaction if its ref is 1 (fresh). Or is already merged and will be cleaned up if its ref is 0 (orphan).
After commit d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots"), reloc tree cleanup is delayed until one block group is balanced.
Since fresh reloc roots are recorded during merge, as long as there is no power loss, those orphan reloc roots converted from fresh ones are handled without problem.
However when power loss happens, orphan reloc roots can be recorded on-disk, thus at next mount time, we will have orphan reloc roots from on-disk data directly, and ignored by clean_dirty_subvols() routine.
Then when background balance starts to balance another block group, and needs to create new reloc root for the same root, btrfs_insert_item() returns -EEXIST, and trigger that BUG_ON().
[FIX] For orphan reloc roots, also queue them to rc->dirty_subvol_roots, so all reloc roots no matter orphan or not, can be cleaned up properly and avoid above BUG_ON().
And to cooperate with above change, clean_dirty_subvols() will check if the queued root is a reloc root or a subvol root. For a subvol root, do the old work, and for a orphan reloc root, clean it up.
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots") CC: stable@vger.kernel.org # 5.1 Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/relocation.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-)
--- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -2161,22 +2161,30 @@ static int clean_dirty_subvols(struct re struct btrfs_root *root; struct btrfs_root *next; int ret = 0; + int ret2;
list_for_each_entry_safe(root, next, &rc->dirty_subvol_roots, reloc_dirty_list) { - struct btrfs_root *reloc_root = root->reloc_root; - - clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state); - list_del_init(&root->reloc_dirty_list); - root->reloc_root = NULL; - if (reloc_root) { - int ret2; - - ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1); + if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) { + /* Merged subvolume, cleanup its reloc root */ + struct btrfs_root *reloc_root = root->reloc_root; + + clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state); + list_del_init(&root->reloc_dirty_list); + root->reloc_root = NULL; + if (reloc_root) { + + ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1); + if (ret2 < 0 && !ret) + ret = ret2; + } + btrfs_put_fs_root(root); + } else { + /* Orphan reloc tree, just clean it up */ + ret2 = btrfs_drop_snapshot(root, NULL, 0, 1); if (ret2 < 0 && !ret) ret = ret2; } - btrfs_put_fs_root(root); } return ret; } @@ -2464,6 +2472,9 @@ again: } } else { list_del_init(&reloc_root->root_list); + /* Don't forget to queue this reloc root for cleanup */ + list_add_tail(&reloc_root->reloc_dirty_list, + &rc->dirty_subvol_roots); } }