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SubjectRe: [PATCH RFC tip/core/rcu 02/10] rcu: make dead code really dead
On Mon, Apr 05, 2010 at 02:49:28PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> > From: Lai Jiangshan <laijs@cn.fujitsu.com>
> >
> > cleanup: make dead code really dead
>
> Is it just me or this spinlock change is more than just a cleanup ? Or
> maybe it just needs a much more descriptive changelog.

Just a cleanup. In the case where the "break" could be executed,
control will never reach the RCU_SAVE_DYNTICK leg of the switch statement.

That said, yes, if control -could- reach the RCU_SAVE_DYNTICK when
this "break" statement was executed, we would have had a locking
problem. But as it is, this change just makes the dead code really
all be dead so that gcc knows not to produce the corresponding binary.

Thanx, Paul

> Thanks,
>
> Mathieu
>
> >
> > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> > kernel/rcutree.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index e54c123..6042fb8 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -1236,11 +1236,11 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
> > break; /* grace period idle or initializing, ignore. */
> >
> > case RCU_SAVE_DYNTICK:
> > -
> > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
> > if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
> > break; /* So gcc recognizes the dead code. */
> >
> > + raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
> > +
> > /* Record dyntick-idle state. */
> > force_qs_rnp(rsp, dyntick_save_progress_counter);
> > raw_spin_lock(&rnp->lock); /* irqs already disabled */
> > --
> > 1.7.0
> >
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com


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