Re: [PATCH rcu 08/15] srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()

[Paul E. McKenney]

On Mon, Nov 11, 2024 at 04:47:49PM +0530, Neeraj Upadhyay wrote:
>  
> > +/**
> > + * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
> > + * @ssp: srcu_struct in which to unregister the old reader.
> > + * @idx: return value from corresponding srcu_read_lock().
> > + *
> > + * Exit a light-weight SRCU read-side critical section.
> > + */
> > +static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
> > +	__releases(ssp)
> > +{
> > +	WARN_ON_ONCE(idx & ~0x1);
> > +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
> > +	srcu_lock_release(&ssp->dep_map);
> > +	__srcu_read_unlock(ssp, idx);
> 
> s/__srcu_read_unlock/__srcu_read_unlock_lite/ ?

Right you are!  I am testing the patch.

The effect of this bug is that srcu_read_unlock_lite() has a needless
memory barrier and fails to check for RCU watching, so not a blazing
emergency.  But it does mean that Andrii was only seeing half of the
performance benefit of using _lite().

							Thanx, Paul