linux-kernel - Re: [PATCH 2/2] target: use RCU_INIT

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Message-ID: <20160502180644.GF3512@linux.vnet.ibm.com>
Date:	Mon, 2 May 2016 11:06:44 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Muhammad Falak R Wani <falakreyaz@...il.com>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	target-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] target: use RCU_INIT_POINTER() when NULLing.

On Mon, May 02, 2016 at 10:59:50AM -0700, Christoph Hellwig wrote:
> On Mon, May 02, 2016 at 10:57:38AM -0700, Paul E. McKenney wrote:
> > -#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
> > +#define rcu_assign_pointer(p, v) \
> > +({ \
> > +	uintptr_t _r_a_p__v = (uintptr_t)(v); \
> > +	\
> > +	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
> > +		WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
> > +	else \
> > +		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
> > +	_r_a_p__v; \
> > +})
> 
> Can't we turn it into an inline (would need different calling
> conventions for p, though).

And for v.  But how do I do that without C++ templates?

Also, does __builtin_constant_p() work reliably on a parameter?
Especially when the compiler decides not to do the inlining?

							Thanx, Paul