[BUG]
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
------

[CAUSE]
The problem is due to the fact that, btrfs block group auto removal only
checks if a block group is unused by checking used_bytes of its block
group item.

However it's possible to have metadata block group whose used bytes is 0,
but has pinned down bytes by delalloc.

In that case, when the delalloc work is ran and quota is enabled, quota
will try to resolve the parents, which could lead to read on tree blocks
in the deleted block group.

[FIX]
Just teach btrfs_delete_unused_bgs() to skip block group who still has
pinned bytes.

Signed-off-by: Qu Wenruo <w...@suse.com>
---
 fs/btrfs/extent-tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f190023386a9..7d14c4ca8232 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10675,7 +10675,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info 
*fs_info)
                /* Don't want to race with allocators so take the groups_sem */
                down_write(&space_info->groups_sem);
                spin_lock(&block_group->lock);
-               if (block_group->reserved ||
+               if (block_group->reserved || block_group->pinned ||
                    btrfs_block_group_used(&block_group->item) ||
                    block_group->ro ||
                    list_is_singular(&block_group->list)) {
-- 
2.17.1

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