On Fri 11-10-19 13:25:25, Sebastian Siewior wrote: > On 2019-08-20 20:01:14 [+0200], Thomas Gleixner wrote: > > On Tue, 20 Aug 2019, Matthew Wilcox wrote: > > > 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? > > > > Christoph requested that: > > > > https://lkml.kernel.org/r/20190802075612.GA20962@xxxxxxxxxxxxx > > What do we do about this one? I was thinking about this for quite some time. In the end I think the patch is almost fine but I'd name the lock b_update_lock and put it just after b_size element in struct buffer_head to use the hole there. That way we don't grow struct buffer_head. With some effort, we could even shrink struct buffer_head from 104 bytes (on x86_64) to 96 bytes but I don't think that effort is worth it (I'd find it better use of time to actually work on getting rid of buffer heads completely). Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
