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-rw-r--r--fs/btrfs/ctree.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 2ee43b6a4f09..539901fb5165 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1014,9 +1014,26 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
if ((root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) && parent)
parent_start = parent->start;
+ /*
+ * If we are COWing a node/leaf from the extent, chunk or device trees,
+ * make sure that we do not finish block group creation of pending block
+ * groups. We do this to avoid a deadlock.
+ * COWing can result in allocation of a new chunk, and flushing pending
+ * block groups (btrfs_create_pending_block_groups()) can be triggered
+ * when finishing allocation of a new chunk. Creation of a pending block
+ * group modifies the extent, chunk and device trees, therefore we could
+ * deadlock with ourselves since we are holding a lock on an extent
+ * buffer that btrfs_create_pending_block_groups() may try to COW later.
+ */
+ if (root == fs_info->extent_root ||
+ root == fs_info->chunk_root ||
+ root == fs_info->dev_root)
+ trans->can_flush_pending_bgs = false;
+
cow = btrfs_alloc_tree_block(trans, root, parent_start,
root->root_key.objectid, &disk_key, level,
search_start, empty_size);
+ trans->can_flush_pending_bgs = true;
if (IS_ERR(cow))
return PTR_ERR(cow);