btrfs: reloc: clear DEAD_RELOC_TREE bit for orphan roots to prevent runaway balance

[BUG]
There are several reported runaway balance, that balance is flooding the
log with "found X extents" where the X never changes.

[CAUSE]
Commit d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after
merge_reloc_roots") introduced BTRFS_ROOT_DEAD_RELOC_TREE bit to
indicate that one subvolume has finished its tree blocks swap with its
reloc tree.

However if balance is canceled or hits ENOSPC halfway, we didn't clear
the BTRFS_ROOT_DEAD_RELOC_TREE bit, leaving that bit hanging forever
until unmount.

Any subvolume root with that bit, would cause backref cache to skip this
tree block, as it has finished its tree block swap.  This would cause
all tree blocks of that root be ignored by balance, leading to runaway
balance.

[FIX]
Fix the problem by also clearing the BTRFS_ROOT_DEAD_RELOC_TREE bit for
the original subvolume of orphan reloc root.

Add an umount check for the stale bit still set.

Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f1143741f6ba057685de32ca6e94e80ba15c0a94..7b66a8e4ca5420cfdcc1d4bb8fcf8020f55840a2 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1994,6 +1994,7 @@ void btrfs_put_root(struct btrfs_root *root)
 
        if (refcount_dec_and_test(&root->refs)) {
                WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
+               WARN_ON(test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state));
                if (root->anon_dev)
                        free_anon_bdev(root->anon_dev);
                btrfs_drew_lock_destroy(&root->snapshot_lock);

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 81b076e4614356f7b264340e0e3a37dad96b7e4a..68dd7a771e5e5206d218515a147e0c8260b799d1 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1935,6 +1935,8 @@ again:
                                        root->reloc_root = NULL;
                                        btrfs_put_root(reloc_root);
                                }
+                               clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
+                                         &root->state);
                                btrfs_put_root(root);
                        }