Messages in this thread |  | | Date | Wed, 10 Aug 2011 16:53:41 +0200 | | From | Frederic Weisbecker <> | | Subject | Re: 3.0-git15 Atomic scheduling in pidmap_init |
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On Wed, Aug 10, 2011 at 08:45:29AM -0400, Josh Boyer wrote: > On Tue, Aug 09, 2011 at 01:35:18PM +0200, Frederic Weisbecker wrote: > > > But setting rdp->qs_pending to 1 in rcu_init_percpu_data() has no effect > > > until a grace period starts. So, if grace periods are prevented from > > Er... really? Because it gets set and __rcu_pending looks at it > unconditionally in the case that is calling set_need_resched. It > doesn't check if there is anything about a grace period going on or not.
You mean this?
if (rdp->qs_pending && !rdp->passed_quiesc) {
/* * If force_quiescent_state() coming soon and this CPU * needs a quiescent state, and this is either RCU-sched * or RCU-bh, force a local reschedule. */ rdp->n_rp_qs_pending++; if (!rdp->preemptible && ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1, jiffies)) set_need_resched(); }
On boot, if we don't start a grace period, we don't schedule a grace period forcing, so rsp->jiffies_force_qs is 0.
With ULONG_CMP_LT taking care of (-1 < jiffies) to be valid even with ulong, then we are fine I guess.
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