[PATCH 4/5] btrfs: add assertion for empty list of transactions at late stage of umount

[fdmanana@kernel.org]

From: Filipe Manana <fdmanana@suse.com>

Add an assertion to close_ctree(), after destroying all the work queues,
to verify we do not have any transaction still open or committing at that
at that point. If we have any, it means something is seriously wrong and
that can cause memory leaks and use-after-free problems. This is motivated
by the previous patches that fixed bugs where we ended up leaking an open
transaction after unmmounting the filesystem.

Tested-by: Fabian Vogt <fvogt@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/disk-io.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index e7bcbd0b93ef..a567d578d0c8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -4181,6 +4181,9 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
 	btrfs_stop_all_workers(fs_info);
 
+	/* We shouldn't have any transaction open at this point. */
+	ASSERT(list_empty(&fs_info->trans_list));
+
 	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
 	free_root_pointers(fs_info, true);
 	btrfs_free_fs_roots(fs_info);
-- 
2.28.0