On Tue 30-07-19 13:24:55, Thomas Gleixner wrote: > 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. > > Substitute the BH_Uptodate_Lock bit spinlock with a regular spinlock for > PREEMPT_RT enabled kernels. > > Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With > the spinlock substitution in place, they can be exposed via > CONFIG_DEBUG_BIT_SPINLOCKS. > > Signed-off-by: Thomas Gleixner <[email protected]> > Cc: "Theodore Ts'o" <[email protected]> > Cc: Alexander Viro <[email protected]> > Cc: Matthew Wilcox <[email protected]> > Cc: [email protected]
Looks good to me. You can add: Reviewed-by: Jan Kara <[email protected]> Honza > --- > fs/buffer.c | 1 + > include/linux/buffer_head.h | 31 +++++++++++++++++++++++++++++++ > 2 files changed, 32 insertions(+) > > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -3360,6 +3360,7 @@ struct buffer_head *alloc_buffer_head(gf > struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags); > if (ret) { > INIT_LIST_HEAD(&ret->b_assoc_buffers); > + buffer_head_init_locks(ret); > preempt_disable(); > __this_cpu_inc(bh_accounting.nr); > recalc_bh_state(); > --- a/include/linux/buffer_head.h > +++ b/include/linux/buffer_head.h > @@ -76,8 +76,35 @@ struct buffer_head { > struct address_space *b_assoc_map; /* mapping this buffer is > associated with */ > atomic_t b_count; /* users using this buffer_head */ > + > +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) > + spinlock_t b_uptodate_lock; > +#endif > }; > > +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) > + > +static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh) > +{ > + unsigned long flags; > + > + spin_lock_irqsave(&bh->b_uptodate_lock, flags); > + return flags; > +} > + > +static inline void > +bh_uptodate_unlock_irqrestore(struct buffer_head *bh, unsigned long flags) > +{ > + spin_unlock_irqrestore(&bh->b_uptodate_lock, flags); > +} > + > +static inline void buffer_head_init_locks(struct buffer_head *bh) > +{ > + spin_lock_init(&bh->b_uptodate_lock); > +} > + > +#else /* PREEMPT_RT || DEBUG_BIT_SPINLOCKS */ > + > static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh) > { > unsigned long flags; > @@ -94,6 +121,10 @@ bh_uptodate_unlock_irqrestore(struct buf > local_irq_restore(flags); > } > > +static inline void buffer_head_init_locks(struct buffer_head *bh) { } > + > +#endif /* !PREEMPT_RT && !DEBUG_BIT_SPINLOCKS */ > + > /* > * macro tricks to expand the set_buffer_foo(), clear_buffer_foo() > * and buffer_foo() functions. > > > -- Jan Kara <[email protected]> SUSE Labs, CR
