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

commit 1dae7e0e58b484eaa43d530f211098fdeeb0f404 upstream.

[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>
[Manually solve the conflicts due to no btrfs root refs rework]
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ee08663380ffd5a45a1c87580fbc305e8413c235)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index ba7061e74feb30e22daf78e44585182cbc06c500..668eb34c1272ec3acc8b0fdcb88c89fe670a72a5 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2540,6 +2540,8 @@ again:
                        if (!IS_ERR(root)) {
                                if (root->reloc_root == reloc_root)
                                        root->reloc_root = NULL;
+                               clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
+                                         &root->state);
                        }
 
                        list_del_init(&reloc_root->root_list);