The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 485df75554257e883d0ce39bb886e8212349748e Mon Sep 17 00:00:00 2001
From: Filipe Manana fdmanana@suse.com Date: Thu, 11 Mar 2021 14:31:06 +0000 Subject: [PATCH] btrfs: always pin deleted leaves when there are active tree mod log users
When freeing a tree block we may end up adding its extent back to the free space cache/tree, as long as there are no more references for it, it was created in the current transaction and writeback for it never happened. This is generally fine, however when we have tree mod log operations it can result in inconsistent versions of a btree after unwinding extent buffers with the recorded tree mod log operations.
This is because:
* We only log operations for nodes (adding and removing key/pointers), for leaves we don't do anything;
* This means that we can log a MOD_LOG_KEY_REMOVE_WHILE_FREEING operation for a node that points to a leaf that was deleted;
* Before we apply the logged operation to unwind a node, we can have that leaf's extent allocated again, either as a node or as a leaf, and possibly for another btree. This is possible if the leaf was created in the current transaction and writeback for it never started, in which case btrfs_free_tree_block() returns its extent back to the free space cache/tree;
* Then, before applying the tree mod log operation, some task allocates the metadata extent just freed before, and uses it either as a leaf or as a node for some btree (can be the same or another one, it does not matter);
* After applying the MOD_LOG_KEY_REMOVE_WHILE_FREEING operation we now get the target node with an item pointing to the metadata extent that now has content different from what it had before the leaf was deleted. It might now belong to a different btree and be a node and not a leaf anymore.
As a consequence, the results of searches after the unwinding can be unpredictable and produce unexpected results.
So make sure we pin extent buffers corresponding to leaves when there are tree mod log users.
CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 78ad31a59e59..36a3c973fda1 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -3323,6 +3323,7 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
if (last_ref && btrfs_header_generation(buf) == trans->transid) { struct btrfs_block_group *cache; + bool must_pin = false;
if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) { ret = check_ref_cleanup(trans, buf->start); @@ -3340,7 +3341,27 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans, goto out; }
- if (btrfs_is_zoned(fs_info)) { + /* + * If this is a leaf and there are tree mod log users, we may + * have recorded mod log operations that point to this leaf. + * So we must make sure no one reuses this leaf's extent before + * mod log operations are applied to a node, otherwise after + * rewinding a node using the mod log operations we get an + * inconsistent btree, as the leaf's extent may now be used as + * a node or leaf for another different btree. + * We are safe from races here because at this point no other + * node or root points to this extent buffer, so if after this + * check a new tree mod log user joins, it will not be able to + * find a node pointing to this leaf and record operations that + * point to this leaf. + */ + if (btrfs_header_level(buf) == 0) { + read_lock(&fs_info->tree_mod_log_lock); + must_pin = !list_empty(&fs_info->tree_mod_seq_list); + read_unlock(&fs_info->tree_mod_log_lock); + } + + if (must_pin || btrfs_is_zoned(fs_info)) { btrfs_redirty_list_add(trans->transaction, buf); pin_down_extent(trans, cache, buf->start, buf->len, 1); btrfs_put_block_group(cache);