diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 813986e38258b7..c3cf3dabe0b1b6 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -3694,15 +3694,29 @@ static int process_dir_items_leaf(struct btrfs_trans_handle *trans, u64 *last_old_dentry_offset) { struct btrfs_root *log = inode->root->log_root; - struct extent_buffer *src = path->nodes[0]; - const int nritems = btrfs_header_nritems(src); + struct extent_buffer *src; + const int nritems = btrfs_header_nritems(path->nodes[0]); const u64 ino = btrfs_ino(inode); bool last_found = false; int batch_start = 0; int batch_size = 0; int i; - for (i = path->slots[0]; i < nritems; i++) { + /* + * We need to clone the leaf, release the read lock on it, and use the + * clone before modifying the log tree. See the comment at copy_items() + * about why we need to do this. + */ + src = btrfs_clone_extent_buffer(path->nodes[0]); + if (!src) + return -ENOMEM; + + i = path->slots[0]; + btrfs_release_path(path); + path->nodes[0] = src; + path->slots[0] = i; + + for (; i < nritems; i++) { struct btrfs_dir_item *di; struct btrfs_key key; int ret; @@ -4303,7 +4317,7 @@ static noinline int copy_items(struct btrfs_trans_handle *trans, { struct btrfs_root *log = inode->root->log_root; struct btrfs_file_extent_item *extent; - struct extent_buffer *src = src_path->nodes[0]; + struct extent_buffer *src; int ret = 0; struct btrfs_key *ins_keys; u32 *ins_sizes; @@ -4314,6 +4328,43 @@ static noinline int copy_items(struct btrfs_trans_handle *trans, const bool skip_csum = (inode->flags & BTRFS_INODE_NODATASUM); const u64 i_size = i_size_read(&inode->vfs_inode); + /* + * To keep lockdep happy and avoid deadlocks, clone the source leaf and + * use the clone. This is because otherwise we would be changing the log + * tree, to insert items from the subvolume tree or insert csum items, + * while holding a read lock on a leaf from the subvolume tree, which + * creates a nasty lock dependency when COWing log tree nodes/leaves: + * + * 1) Modifying the log tree triggers an extent buffer allocation while + * holding a write lock on a parent extent buffer from the log tree. + * Allocating the pages for an extent buffer, or the extent buffer + * struct, can trigger inode eviction and finally the inode eviction + * will trigger a release/remove of a delayed node, which requires + * taking the delayed node's mutex; + * + * 2) Allocating a metadata extent for a log tree can trigger the async + * reclaim thread and make us wait for it to release enough space and + * unblock our reservation ticket. The reclaim thread can start + * flushing delayed items, and that in turn results in the need to + * lock delayed node mutexes and in the need to write lock extent + * buffers of a subvolume tree - all this while holding a write lock + * on the parent extent buffer in the log tree. + * + * So one task in scenario 1) running in parallel with another task in + * scenario 2) could lead to a deadlock, one wanting to lock a delayed + * node mutex while having a read lock on a leaf from the subvolume, + * while the other is holding the delayed node's mutex and wants to + * write lock the same subvolume leaf for flushing delayed items. + */ + src = btrfs_clone_extent_buffer(src_path->nodes[0]); + if (!src) + return -ENOMEM; + + i = src_path->slots[0]; + btrfs_release_path(src_path); + src_path->nodes[0] = src; + src_path->slots[0] = i; + ins_data = kmalloc(nr * sizeof(struct btrfs_key) + nr * sizeof(u32), GFP_NOFS); if (!ins_data)