[PATCH AUTOSEL 5.4 187/330] btrfs: do not init a reloc root if we aren't relocating

Sasha Levin
2020-09-18T02:05:06Z

From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit 2abc726ab4b83db774e315c660ab8da21477092f ]

We previously were checking if the root had a dead root before accessing
root->reloc_root in order to avoid a use-after-free type bug. However
this scenario happens after we've unset the reloc control, so we would
have been saved if we'd simply checked for fs_info->reloc_control. At
this point during relocation we no longer need to be creating new reloc
roots, so simply move this check above the reloc_root checks to avoid
any future races and confusion.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/relocation.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index af3605a0bf2e0..1313506a7ecb5 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1468,6 +1468,10 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
int clear_rsv = 0;
int ret;

+ if (!rc || !rc->create_reloc_tree ||
+ root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
+ return 0;
+
/*
* The subvolume has reloc tree but the swap is finished, no need to
* create/update the dead reloc tree
@@ -1481,10 +1485,6 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
return 0;
}

- if (!rc || !rc->create_reloc_tree ||
- root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
- return 0;
-
if (!trans->reloc_reserved) {
rsv = trans->block_rsv;
trans->block_rsv = rc->block_rsv;
@@ -2336,6 +2336,18 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
trans = NULL;
goto out;
}
+
+ /*
+ * At this point we no longer have a reloc_control, so we can't
+ * depend on btrfs_init_reloc_root to update our last_trans.
+ *
+ * But that's ok, we started the trans handle on our
+ * corresponding fs_root, which means it's been added to the
+ * dirty list. At commit time we'll still call
+ * btrfs_update_reloc_root() and update our root item
+ * appropriately.
+ */
+ reloc_root->last_trans = trans->transid;
trans->block_rsv = rc->block_rsv;

replaced = 0;
--
2.25.1