linux-kernel - [PATCH tip/core/rcu 5/6] rcu: Exclude RCU-offline CPUs from expedited grace periods

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Message-Id: <1471879387-7902-5-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Mon, 22 Aug 2016 08:23:06 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
        bobby.prani@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 5/6] rcu: Exclude RCU-offline CPUs from expedited grace periods

The expedited RCU grace periods currently rely on a failure indication
from smp_call_function_single() to determine that a given CPU is offline.
This works after a fashion, but is more contorted and less precise than
relying on RCU's internal state.  This commit therefore takes a first
step towards relying on internal state.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree_exp.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index f316683b18f1..3bc4b3dda801 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -359,7 +359,8 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
 
 			if (raw_smp_processor_id() == cpu ||
-			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
+			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1) ||
+			    !(rnp->qsmaskinitnext & rdp->grpmask))
 				mask_ofl_test |= rdp->grpmask;
 		}
 		mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
-- 
2.5.2