[PATCH 2/5] btrfs: restart relocate_tree_blocks properly

From: Josef Bacik <josef@toxicpanda.com>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH 2/5] btrfs: restart relocate_tree_blocks properly
Date: Fri, 20 Mar 2020 14:34:33 -0400	[thread overview]
Message-ID: <20200320183436.16908-3-josef@toxicpanda.com> (raw)
In-Reply-To: <20200320183436.16908-1-josef@toxicpanda.com>

There are two bugs here, but fixing them independently would just result
in pain if you happened to bisect between the two patches.

First is how we handle the -EAGAIN from relocate_tree_block().  We don't
set error, unless we happen to be the first node, which makes 0 sense, I
have no idea what the code was trying to accomplish here.

We in fact _do_ want err set here so that we know we need to restart in
relocate_block_group().  Also we need finish_pending_nodes() to not
actually call link_to_upper(), because we didn't actually relocate the
block.

And then if we do get -EAGAIN we do not want to set our backref cache
last_trans to the one before ours.  This would force us to update our
backref cache if we didn't cross trans id's, which would mean we'd have
some nodes updated to their new_bytenr, but still able to find their old
bytenr because we're searching the same commit root as the last time we
went through relocate_tree_blocks.

Fixing these two things keeps us from panicing when we start breaking
out of relocate_tree_blocks() either for delayed ref flushing or enospc.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/relocation.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index df33649c592c..66a344df4f05 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3226,9 +3226,8 @@ int relocate_tree_blocks(struct btrfs_trans_handle *trans,
 		ret = relocate_tree_block(trans, rc, node, &block->key,
 					  path);
 		if (ret < 0) {
-			if (ret != -EAGAIN || &block->rb_node == rb_first(blocks))
-				err = ret;
-			goto out;
+			err = ret;
+			break;
 		}
 	}
 out:
@@ -4204,12 +4203,6 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
 		if (!RB_EMPTY_ROOT(&blocks)) {
 			ret = relocate_tree_blocks(trans, rc, &blocks);
 			if (ret < 0) {
-				/*
-				 * if we fail to relocate tree blocks, force to update
-				 * backref cache when committing transaction.
-				 */
-				rc->backref_cache.last_trans = trans->transid - 1;
-
 				if (ret != -EAGAIN) {
 					err = ret;
 					break;
-- 
2.24.1

