On Tue, Jul 08, 2014 at 04:43:37PM -0400, Pranith Kumar wrote:
> On Tue, Jul 8, 2014 at 4:35 PM, Paul E. McKenney
> <[email protected]> wrote:
> >
> > Good catch, I clearly didn't include enough patterns in my search.
> >
> > But please see below. And please rebase onto branch rcu/dev in
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git,
> > as this patch set does not apply.
>
> OK, I will resend the patch. One question below:
>
> >
> > Thanx, Paul
> >
> >> Signed-off-by: Pranith Kumar <[email protected]>
> >> ---
> >> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> >> index dac6d20..f500395 100644
> >> --- a/kernel/rcu/tree.c
> >> +++ b/kernel/rcu/tree.c
> >> @@ -1700,7 +1700,7 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int
> >> fqs_state_in)
> >> if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
> >> raw_spin_lock_irq(&rnp->lock);
> >> smp_mb__after_unlock_lock();
> >> - ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;
> >> + ACCESS_ONCE(rsp->gp_flags) = rsp->gp_flags &
> >> ~RCU_GP_FLAG_FQS;
> >
> > Here we need ACCESS_ONCE() around both instances of rsp->gp_flags.
>
> I see that all accesses of gp_flags are wrapped with ACCESS_ONCE(). Is
> there any reason why we can't declare it as 'volatile' and not use
> ACCESS_ONCE everywhere?
The explicit ACCESS_ONCE() serves as a good documentation aid.
Thanx, Paul
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