[PATCH AUTOSEL 5.7 55/60] btrfs: qgroup: free per-trans reserved space when a subvolume gets dropped

Sasha Levin
2020-08-10T19:26:51Z

From: Qu Wenruo <wqu@suse.com>

[ Upstream commit a3cf0e4342b6af9e6b34a4b913c630fbd03a82ea ]

[BUG]
Sometime fsstress could lead to qgroup warning for case like
generic/013:

BTRFS warning (device dm-3): qgroup 0/259 has unreleased space, type 1 rsv 81920
------------[ cut here ]------------
WARNING: CPU: 9 PID: 24535 at fs/btrfs/disk-io.c:4142 close_ctree+0x1dc/0x323 [btrfs]
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:close_ctree+0x1dc/0x323 [btrfs]
Call Trace:
btrfs_put_super+0x15/0x17 [btrfs]
generic_shutdown_super+0x72/0x110
kill_anon_super+0x18/0x30
btrfs_kill_super+0x17/0x30 [btrfs]
deactivate_locked_super+0x3b/0xa0
deactivate_super+0x40/0x50
cleanup_mnt+0x135/0x190
__cleanup_mnt+0x12/0x20
task_work_run+0x64/0xb0
__prepare_exit_to_usermode+0x1bc/0x1c0
__syscall_return_slowpath+0x47/0x230
do_syscall_64+0x64/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
---[ end trace 6c341cdf9b6cc3c1 ]---
BTRFS error (device dm-3): qgroup reserved space leaked

While that subvolume 259 is no longer in that filesystem.

[CAUSE]
Normally per-trans qgroup reserved space is freed when a transaction is
committed, in commit_fs_roots().

However for completely dropped subvolume, that subvolume is completely
gone, thus is no longer in the fs_roots_radix, and its per-trans
reserved qgroup will never be freed.

Since the subvolume is already gone, leaked per-trans space won't cause
any trouble for end users.

[FIX]
Just call btrfs_qgroup_free_meta_all_pertrans() before a subvolume is
completely dropped.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/extent-tree.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 54a64d1e18c6b..7c86188b33d43 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5481,6 +5481,14 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
}
}

+ /*
+ * This subvolume is going to be completely dropped, and won't be
+ * recorded as dirty roots, thus pertrans meta rsv will not be freed at
+ * commit transaction time. So free it here manually.
+ */
+ btrfs_qgroup_convert_reserved_meta(root, INT_MAX);
+ btrfs_qgroup_free_meta_all_pertrans(root);
+
if (test_bit(BTRFS_ROOT_IN_RADIX, &root->state))
btrfs_add_dropped_root(trans, root);
else
--
2.25.1