Messages in this thread | | | Date | Wed, 23 Jul 2014 05:23:35 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp_flags for spurious wakeup |
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On Wed, Jul 23, 2014 at 01:09:47AM -0400, Pranith Kumar wrote: > rcu_gp_init() is called once the gp_kthread wakes up on the condition that > the init bit is set in the gp_flags. For a spurious wakeup we need to check that > it is actually set. This commit ensures that the RCU_GP_FLAG_INIT bit is set in > gp_flags. > > Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
The trick here is that the other bits have no meaning if we are not yet in a grace period. If any get spuriously set, for example, by a race between force_quiescent_state() and the end of a grace period, we really do want to clear them all.
So sorry, but no.
Thanx, Paul
> --- > kernel/rcu/tree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 8d598a2..f8847d9 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1600,7 +1600,7 @@ static int rcu_gp_init(struct rcu_state *rsp) > rcu_bind_gp_kthread(); > raw_spin_lock_irq(&rnp->lock); > smp_mb__after_unlock_lock(); > - if (!ACCESS_ONCE(rsp->gp_flags)) { > + if (!(ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_INIT)) { > /* Spurious wakeup, tell caller to go back to sleep. */ > raw_spin_unlock_irq(&rnp->lock); > return 0; > -- > 2.0.0.rc2 >
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