On Wed, Jul 01, 2015 at 07:03:13AM -0700, Paul E. McKenney wrote: > On Wed, Jul 01, 2015 at 03:48:06PM +0200, Peter Zijlstra wrote: > > On Wed, Jul 01, 2015 at 06:41:44AM -0700, Paul E. McKenney wrote: > > > On Wed, Jul 01, 2015 at 12:05:21PM +0200, Peter Zijlstra wrote: > > > > On Tue, Jun 30, 2015 at 02:48:27PM -0700, Paul E. McKenney wrote: > > > > > rsp->gp_state = RCU_GP_WAIT_FQS; > > > > > ret = > > > > > wait_event_interruptible_timeout(rsp->gp_wq, > > > > > + ((gf = READ_ONCE(rsp->gp_flags)) & > > > > > + RCU_GP_FLAG_FQS) || > > > > > + (!READ_ONCE(rnp->qsmask) && > > > > > + !rcu_preempt_blocked_readers_cgp(rnp)) > > > > > || > > > > > + rcu_exp_gp_seq_done(rsp->exp_rsp, > > > > > + rsp->gp_exp_snap), > > > > > + j); > > > > > rsp->gp_state = RCU_GP_DONE_FQS; > > > > > > > > How can the GP be done if we timed out or got interrupted? > > > > > > If all the CPUs still blocking the grace period went idle, or in a > > > NO_HZ_FULL kernel, entered nohz_full userspace execution. Or, if > > > certain low-probability races happen, went offline. > > > > But what if none of those are true and we still timed out? You > > unconditionally grant the GP. > > Say what??? > > I recheck the conditions and break out of the loop only if one or more > of the grace-period-end conditions is satisfied. If not, I invoke > rcu_gp_fqs() to do the scan to see if all remaining CPUs are idle, > in nohz_full userspace execution, or offline. > > What am I mising here?
The whole wait_event_interruptible_timeout() thing can end without @cond being true, after which you unconditionally set ->gp_state = RCU_GP_DONE_FQS. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
