On Tue, Jul 18, 2023 at 09:48:59PM -0400, Joel Fernandes wrote:
>
>
> 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?
Either that or the people who removed uses injected bugs...
But if this one really does go away, do we need ->pprev to be
protected by _ONCE()?
Thanx, Paul
