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

From: Paul E. McKenney
Date: Thu Mar 20 2014 - 11:06:17 EST

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(
> >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

Thanx, Paul

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at