| Message ID | 20190730120321.393759046@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fs: Substitute bit-spinlocks for PREEMPT_RT and debugging | expand |
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 <tglx@linutronix.de> > Cc: "Theodore Ts'o" <tytso@mit.edu> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: linux-fsdevel@vger.kernel.org Looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> 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. > > >
--- 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.
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 <tglx@linutronix.de> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Matthew Wilcox <willy@infradead.org> Cc: linux-fsdevel@vger.kernel.org --- fs/buffer.c | 1 + include/linux/buffer_head.h | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+)