Debug closures

configname: CONFIG_BCACHE_CLOSURES_DEBUG

Linux Kernel Configuration
└─>Device Drivers
└─>Multiple devices driver support (RAID and LVM)
└─>Debug closures
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Keeps all active closures in a linked list and provides a debugfs
interface to list them, which makes it possible to see asynchronous
operations that get stuck.