On 30.05.2018 07:40, Qu Wenruo wrote:
> Under certain KVM load and LTP tests, we are possible to hit the
> following calltrace if quota is enabled:
> ------
> BTRFS critical (device vda2): unable to find logical 8820195328 length 4096
> BTRFS critical (device vda2): unable to find logical 8820195328 length 4096
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 49 at ../block/blk-core.c:172 blk_status_to_errno+0x1a/0x30
> CPU: 0 PID: 49 Comm: kworker/u2:1 Not tainted 4.12.14-15-default #1 SLE15 (unreleased)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
> Workqueue: btrfs-endio-write btrfs_endio_write_helper [btrfs]
> task: ffff9f827b340bc0 task.stack: ffffb4f8c0304000
> RIP: 0010:blk_status_to_errno+0x1a/0x30
> Call Trace:
> submit_extent_page+0x191/0x270 [btrfs]
> ? btrfs_create_repair_bio+0x130/0x130 [btrfs]
> __do_readpage+0x2d2/0x810 [btrfs]
> ? btrfs_create_repair_bio+0x130/0x130 [btrfs]
> ? run_one_async_done+0xc0/0xc0 [btrfs]
> __extent_read_full_page+0xe7/0x100 [btrfs]
> ? run_one_async_done+0xc0/0xc0 [btrfs]
> read_extent_buffer_pages+0x1ab/0x2d0 [btrfs]
> ? run_one_async_done+0xc0/0xc0 [btrfs]
> btree_read_extent_buffer_pages+0x94/0xf0 [btrfs]
> read_tree_block+0x31/0x60 [btrfs]
> read_block_for_search.isra.35+0xf0/0x2e0 [btrfs]
> btrfs_search_slot+0x46b/0xa00 [btrfs]
> ? kmem_cache_alloc+0x1a8/0x510
> ? btrfs_get_token_32+0x5b/0x120 [btrfs]
> find_parent_nodes+0x11d/0xeb0 [btrfs]
> ? leaf_space_used+0xb8/0xd0 [btrfs]
> ? btrfs_leaf_free_space+0x49/0x90 [btrfs]
> ? btrfs_find_all_roots_safe+0x93/0x100 [btrfs]
> btrfs_find_all_roots_safe+0x93/0x100 [btrfs]
> btrfs_find_all_roots+0x45/0x60 [btrfs]
> btrfs_qgroup_trace_extent_post+0x20/0x40 [btrfs]
> btrfs_add_delayed_data_ref+0x1a3/0x1d0 [btrfs]
> btrfs_alloc_reserved_file_extent+0x38/0x40 [btrfs]
> insert_reserved_file_extent.constprop.71+0x289/0x2e0 [btrfs]
> btrfs_finish_ordered_io+0x2f4/0x7f0 [btrfs]
> ? pick_next_task_fair+0x2cd/0x530
> ? __switch_to+0x92/0x4b0
> btrfs_worker_helper+0x81/0x300 [btrfs]
> process_one_work+0x1da/0x3f0
> worker_thread+0x2b/0x3f0
> ? process_one_work+0x3f0/0x3f0
> kthread+0x11a/0x130
> ? kthread_create_on_node+0x40/0x40
> ret_from_fork+0x35/0x40
> Code: 00 00 5b c3 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 40 80 ff 0c 40 0f b6 c7 77 0b 48 c1 e0 04 8b 80 00 bf c8 bd c3 <0f> 0b b8 fb ff ff ff c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00
> ---[ end trace f079fb809e7a862b ]---
> BTRFS critical (device vda2): unable to find logical 8820195328 length 16384
> BTRFS: error (device vda2) in btrfs_finish_ordered_io:3023: errno=-5 IO failure
> BTRFS info (device vda2): forced readonly
> BTRFS error (device vda2): pending csums is 2887680
> ------
>
> Although we haven't hit the same bug in real world, it shows that since
> qgroup is heavily relying on commit root, if block group auto removal
> happens and removed the empty block group, qgroup could failed to find
> its old referencers.
But why does qgroup care about the old references, if they are going to
be freed doesn't this mean their reference is going to be unaccounted?
>
> This patch will add a new member for btrfs_transaction,
> pending_unused_bgs.
> Now unused bgs will go trans->transaction->pending_unused_bgs, then
> fs_info->unused_bgs, and finally get removed by
> btrfs_deleted_unused_bgs().
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/ctree.h | 3 ++-
> fs/btrfs/extent-tree.c | 34 ++++++++++++++++++++++++++++++----
> fs/btrfs/scrub.c | 2 +-
> fs/btrfs/transaction.c | 7 +++++++
> fs/btrfs/transaction.h | 10 ++++++++++
> 5 files changed, 50 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 9431ed7b7cd1..02eee472fbd2 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2827,7 +2827,8 @@ void check_system_chunk(struct btrfs_trans_handle *trans,
> struct btrfs_fs_info *fs_info, const u64 type);
> u64 add_new_free_space(struct btrfs_block_group_cache *block_group,
> u64 start, u64 end);
> -void btrfs_mark_bg_unused(struct btrfs_block_group_cache *bg);
> +void btrfs_mark_bg_unused(struct btrfs_block_group_cache *bg,
> + struct btrfs_trans_handle *trans);
>
> /* ctree.c */
> int btrfs_bin_search(struct extent_buffer *eb, const struct btrfs_key *key,
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 31627de751d1..3d468ed0e071 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -6294,7 +6294,7 @@ static int update_block_group(struct btrfs_trans_handle *trans,
> * cache writeout.
> */
> if (!alloc && old_val == 0)
> - btrfs_mark_bg_unused(cache);
> + btrfs_mark_bg_unused(cache, trans);
>
> btrfs_put_block_group(cache);
> total -= num_bytes;
> @@ -10136,7 +10136,7 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
> inc_block_group_ro(cache, 1);
> } else if (btrfs_block_group_used(&cache->item) == 0) {
> ASSERT(list_empty(&cache->bg_list));
> - btrfs_mark_bg_unused(cache);
> + btrfs_mark_bg_unused(cache, NULL);
> }
> }
>
> @@ -11055,15 +11055,41 @@ void btrfs_wait_for_snapshot_creation(struct btrfs_root *root)
> }
> }
>
> -void btrfs_mark_bg_unused(struct btrfs_block_group_cache *bg)
> +/*
> + * Get a block group cache and mark it as unused (if not already
> + * unused/deleted)
> + *
> + * NOTE:
> + * Since qgroup could search commit root at any time, we can't just
> + * delete the block group and its chunk mapping in current trans.
> + * So we record bgs to be deleted in trans->transaction and then
> + * queue them into fs_info->unused_bgs.
> + *
> + * @bg: The block group cache
> + * @trans: The trans handler
> + */
> +void btrfs_mark_bg_unused(struct btrfs_block_group_cache *bg,
> + struct btrfs_trans_handle *trans)
> {
> struct btrfs_fs_info *fs_info = bg->fs_info;
>
> spin_lock(&fs_info->unused_bgs_lock);
> if (list_empty(&bg->bg_list)) {
> + /*
> + * Get one reference, will be freed at btrfs_delete_unused_bgs()
> + */
> btrfs_get_block_group(bg);
> trace_btrfs_add_unused_block_group(bg);
> - list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
> +
> + /*
> + * If we don't have a trans, it means we are at mount time.
> + * It's completely fine to mark it ready to be deleted.
> + */
> + if (!trans)
> + list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
> + else
> + list_add_tail(&bg->bg_list,
> + &trans->transaction->pending_unused_bgs);
> }
> spin_unlock(&fs_info->unused_bgs_lock);
> }
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 40086b47a65f..d9e2420da457 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -3981,7 +3981,7 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
> if (!cache->removed && !cache->ro && cache->reserved == 0 &&
> btrfs_block_group_used(&cache->item) == 0) {
> spin_unlock(&cache->lock);
> - btrfs_mark_bg_unused(cache);
> + btrfs_mark_bg_unused(cache, NULL);
> } else {
> spin_unlock(&cache->lock);
> }
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index 4485eae41e88..4bead1fd1006 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -264,6 +264,7 @@ static noinline int join_transaction(struct btrfs_fs_info *fs_info,
>
> INIT_LIST_HEAD(&cur_trans->pending_snapshots);
> INIT_LIST_HEAD(&cur_trans->pending_chunks);
> + INIT_LIST_HEAD(&cur_trans->pending_unused_bgs);
> INIT_LIST_HEAD(&cur_trans->switch_commits);
> INIT_LIST_HEAD(&cur_trans->dirty_bgs);
> INIT_LIST_HEAD(&cur_trans->io_bgs);
> @@ -2262,6 +2263,12 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
> wake_up(&cur_trans->commit_wait);
> clear_bit(BTRFS_FS_NEED_ASYNC_COMMIT, &fs_info->flags);
>
> + /* transaction is done, queue pending unused bgs to cleaner */
> + spin_lock(&fs_info->unused_bgs_lock);
> + list_splice_tail_init(&cur_trans->pending_unused_bgs,
> + &fs_info->unused_bgs);
> + spin_unlock(&fs_info->unused_bgs_lock);
> +
> spin_lock(&fs_info->trans_lock);
> list_del_init(&cur_trans->list);
> spin_unlock(&fs_info->trans_lock);
> diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
> index d8c0826bc2c7..9f160e1811f7 100644
> --- a/fs/btrfs/transaction.h
> +++ b/fs/btrfs/transaction.h
> @@ -57,6 +57,16 @@ struct btrfs_transaction {
> struct list_head switch_commits;
> struct list_head dirty_bgs;
>
> + /*
> + * Unused block groups waiting to be deleted after current transaction.
> + * Protected by fs_info->unused_bgs_lock.
> + *
> + * Since qgroup could search commit root, we can't delete unused block
> + * group in the same trans when it get emptied, but delay it to next
> + * transaction (or next mount if power loss happens)
> + */
> + struct list_head pending_unused_bgs;
> +
> /*
> * There is no explicit lock which protects io_bgs, rather its
> * consistency is implied by the fact that all the sites which modify
>
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