Re: [PATCH rcu 6/6] rcu: Use WRITE_ONCE() for assignments to ->next for rculist_nulls

[Joel Fernandes]

On 7/18/23 14:32, Paul E. McKenney wrote:
> On Tue, Jul 18, 2023 at 10:48:07PM +0800, Alan Huang wrote:
> > > 2023年7月18日 21:49，Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> 写道：
> > >
> > > On 7/17/23 14:03, Paul E. McKenney wrote:
> > > > From: Alan Huang <mmpgouride@xxxxxxxxx>
> > > > When the objects managed by rculist_nulls are allocated with
> > > > SLAB_TYPESAFE_BY_RCU, old readers may still hold references to an object
> > > > even though it is just now being added, which means the modification of
> > > > ->next is visible to readers.  This patch therefore uses WRITE_ONCE()
> > > > for assignments to ->next.
> > > > Signed-off-by: Alan Huang <mmpgouride@xxxxxxxxx>
> > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > >
> > > Did we ever conclude that the READ_ONCE() counterparts were not needed? ;-)
> >
> > Read-side is already protected by rcu_dereference_raw() in hlist_nulls_for_each_entry_{rcu, safe}.
>
> It turns out that different traversal synchronization designs want
> different pointers using WRITE_ONCE().

Thank you Alan and Paul,

Btw, I don't see any users of hlist_nulls_unhashed_lockless(), maybe it 
can be removed?

 - Joel