From 1dae7e0e58b484eaa43d530f211098fdeeb0f404 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Wed, 20 May 2020 14:58:51 +0800
Patch-mainline: v5.8-rc1
Git-commit: 1dae7e0e58b484eaa43d530f211098fdeeb0f404
References: bsc#1171417 bsc#1160947 bsc#1172366
Subject: [PATCH 2/2] 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>
---
 fs/btrfs/relocation.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2540,6 +2540,8 @@ again:
 				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);