Re: [PATCH] fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular spinlock_t

[Matthew Wilcox]

On Tue, Aug 20, 2019 at 07:08:18PM +0200, Sebastian Siewior wrote:
> Bit spinlocks are problematic if PREEMPT_RT is enabled, because 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. So RT
> replaces the bit spinlocks with regular spinlocks to avoid this problem.
> Bit spinlocks are also not covered by lock debugging, e.g. lockdep.
> 
> Substitute the BH_Uptodate_Lock bit spinlock with a regular spinlock.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> [bigeasy: remove the wrapper and use always spinlock_t]

Uhh ... always grow the buffer_head, even for non-PREEMPT_RT?  Why?