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@xxxxxxxxxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
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 <jack@xxxxxxxx>
SUSE Labs, CR
