Hello, This series is derived from Thomas' series to get rid of bit spinlocks in buffer head code. These patches convert BH_State bit spinlock to an ordinary spinlock inside struct journal_head and somewhat reduce the critical section under BH_JournalHead bit spinlock so that it is fine for RT. Motivation from original Thomas' series: Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable preemption, which is undesired for latency reasons and breaks when regular spinlocks are taken within the bit_spinlock locked region because regular spinlocks are converted to 'sleeping spinlocks' on RT. Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With the spinlock substitution in place, they can be exposed via a new config switch: CONFIG_DEBUG_BIT_SPINLOCKS. Ted, can you pick up these patches? Thanks! Changes since v1: * Fixed up compilation breakage on UP due to missing linux/spinlock.h include Honza
