Re: [PATCH 0/9] Replace rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x,NULL)

[Arend van Spriel]

On 03/20/14 16:06, Paul E. McKenney wrote:
> On Thu, Mar 20, 2014 at 03:58:52PM +0100, Arend van Spriel wrote:
> > On 20/03/14 15:37, Monam Agarwal wrote:
> > > This patchset uses following coccinelle script to replace
> > > rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x,NULL)
> > >
> > > @@
> > > expression E;
> > > @@
> > > - rcu_assign_pointer(
> > > + RCU_INIT_POINTER(
> > > E, NULL)
> >
> > I am not very familiar with rcu functionality nor coccinelle, but it
> > looks too generic. I would think only NULL assignments during
> > initialization should use RCU_INIT_POINTER(). The first patch in the
> > series does it in a function called unregister_...(). Is it really
> > ok to do there?
>
> Hello, Arend,
>
> The thing that rcu_assign_pointer() is doing is ensuring that the
> initialization of a structure is carried out before storing a pointer
> to that structure.  In the case of the NULL pointer, there is no
> structure to initialize, so nothing need be ordered.
>
> So, yes, rcu_assign_pointer(p, NULL) can always safely be converted to
> RCU_INIT_POINTER(p, NULL).  ;-)

And so I learned something today. Thanks, Paul. I really should pick up 
reading rcu material again. It ended up in a dusty corner upstairs.

Thanks,
Arend
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