This is on a Fedora 30 system. I have tested with both 5.1 and 5.2 with the same result. Kernels 4.20 and older have worked fine. Not sure where to start debugging the issue. Here is an example stack of Vim hanging when trying to do a write to the filesystem.
[<0>] pagecache_get_page+0x196/0x370 [<0>] io_ctl_prepare_pages+0x4b/0x140 [btrfs] [<0>] __load_free_space_cache+0x1e1/0x600 [btrfs] [<0>] load_free_space_cache+0xc1/0x170 [btrfs] [<0>] cache_block_group+0x1b4/0x3d0 [btrfs] [<0>] find_free_extent+0x901/0xff0 [btrfs] [<0>] btrfs_reserve_extent+0xea/0x190 [btrfs] [<0>] __btrfs_prealloc_file_range+0x11d/0x490 [btrfs] [<0>] cache_save_setup+0x229/0x3d0 [btrfs] [<0>] btrfs_start_dirty_block_groups+0x1e2/0x4d0 [btrfs] [<0>] btrfs_commit_transaction+0xba/0x9a0 [btrfs] [<0>] btrfs_sync_file+0x32b/0x420 [btrfs] [<0>] do_fsync+0x38/0x70 [<0>] __x64_sys_fsync+0x10/0x20 [<0>] do_syscall_64+0x5f/0x1a0 [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
